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Tricks of Atomic Structure and Radioactivity for NDA

Dalton's Atomic Theory and Subatomic Particles

Q 1763856745

Which of the following statements about the electron is incorrect?
NCERT Exemplar
(A)

It is a negatively charged particle

(B)

The mass of electron is equal to the mass of neutron

(C)

It is a basic constituent of all atoms

(D)

It is a constituent of cathode rays

Solution:

The mass of electron is very small as compared to the mass of the neutron


Mass of electron `= 9.1xx10^(-31)kg`

Mass of neutron `= 1.67xx10^(-27)kg `
Correct Answer is `=>` (B) The mass of electron is equal to the mass of neutron
Q 2877567486

According to Dalton's atomic theory the smallest particle which is capable of independent existence is

(A)

element

(B)

atom

(C)

molecule

(D)

ion

Solution:

The mass of electron is very small as compared to the mass of the neutron


Mass of electron `= 9.1xx10^(-31)kg`

Mass of neutron `= 1.67xx10^(-27)kg `
Correct Answer is `=>` (B) atom
Q 2887567487

Electron was discovered by

(A)

Crookes

(B)

J. J. Thomson

(C)

Henry

(D)

Rutherford

Solution:

The mass of electron is very small as compared to the mass of the neutron


Mass of electron `= 9.1xx10^(-31)kg`

Mass of neutron `= 1.67xx10^(-27)kg `
Correct Answer is `=>` (B) J. J. Thomson
Q 1743856743

Which of the following statement is not correct about the characteristics of cathode rays ?
NCERT Exemplar
(A)

They start from the cathode and move towards the anode

(B)

They travel in straight line in the absence of an external electrical or magnetic field

(C)

Characteristics of cathode rays do not depend upon the material of electrodes in cathode ray tube

(D)

Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube

Solution:

Cathode rays consist of negatively charged material particles called electrons. It was
discovered by William Crookes. The characteristics of cathode rays do not depend
upon the material of electrodes and the nature of the gas present in the cathode ray
tube.
Correct Answer is `=>` (D) Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube
Q 2847667583

Which of the following is the correct sequence in terms of increasing mass?

(A)

Proton electron alpha particle hydrogen atom

(B)

Electron, proton, hydrogen atom, alpha particle

(C)

Hydrogen atom. proton. electron, alpha particle

(D)

Alpha particle, proton. hydrogen atom electron

Solution:

Cathode rays consist of negatively charged material particles called electrons. It was
discovered by William Crookes. The characteristics of cathode rays do not depend
upon the material of electrodes and the nature of the gas present in the cathode ray
tube.
Correct Answer is `=>` (B) Electron, proton, hydrogen atom, alpha particle

Atomic Models

Q 1783856747

Which of the following properties of atom could be explained correctly by Thomson model of atom?
NCERT Exemplar
(A)

Overall neutrality of atom

(B)

Spectra of hydrogen atom

(C)

Position of electrons, protons and neutrons in atom

(D)

Stability of atom

Solution:

J J Thomson, in 1898, proposed plum pudding, (raisin pudding or watermelon) model
of atom. An important feature of this model is that the mass of the atom is assumed to
be uniformly distributed over the atom. This model was able to explain the overall
neutrality of the atom.
Correct Answer is `=>` (A) Overall neutrality of atom
Q 2807667588

Bohr's theory is applicable to

(A)

H - atom

(B)

`He^+` ion

(C)

`Li^(2+)` ions

(D)

All of these

Solution:

J J Thomson, in 1898, proposed plum pudding, (raisin pudding or watermelon) model
of atom. An important feature of this model is that the mass of the atom is assumed to
be uniformly distributed over the atom. This model was able to explain the overall
neutrality of the atom.
Correct Answer is `=>` (D) All of these
Q 2817667589

According to Bohr's model of an element

(A)

`mvr = (n h)/(2pi)`

(B)

`mvr = (2pi)/(n h)`

(C)

`mvr = (n^2 h^2)/(2pi^2)`

(D)

`mvr^2 = (n h)/pi`

Solution:

Angular momentum `mvr = ( n h)/(2pi)`
Correct Answer is `=>` (A) `mvr = (n h)/(2pi)`
Q 2827167981

Following questions consist of two statements labelled as Statement I and Statement II. Examine both the Statements carefully and mark the correct choice according to the codes given below.
Statement I : An atom is electrically neutral.
Statement II : Atoms contain equal number of proton and neutron.

(A)

Both the statements are true and Statement II is the correct explanation of Statement I

(B)

Both the statements are true but Statement II is not the correct explanation of Statement I.

(C)

Statement I is true, but Statement II is false

(D)

Statement I is false, but Statement II is true.

Solution:

Angular momentum `mvr = ( n h)/(2pi)`
Correct Answer is `=>` (C) Statement I is true, but Statement II is false
Q 1763023845

Which of the following conclusions could not be derived from Rutherford's `alpha`-particle scattering experiment?
NCERT Exemplar
(A)

Most of the space in the atom is empty

(B)

The radius of the atom is about`10^(-10)` m while that of nucleus is`10^(-15)` m

(C)

Electrons move in a circular path of fixed energy called orbits

(D)

Electrons and the nucleus are held together by electrostatic forces of attraction

Solution:

Concept of electrons move in a circular path of fixed energy called orbits was put
forward by Bohr and not derived from Rutherford's scattering experiment.
Out of a large number of circular orbits theoretically possible around the nucleus, the
electron revolve only in those orbits which have a tired value of energy. Hence, these
orbits are called energy level or stationary states
Correct Answer is `=>` (C) Electrons move in a circular path of fixed energy called orbits
Q 2847767683

Which of the following statements does not form part of Bohr's model of the hydrogen atom?

(A)

Energy of the electrons in the orbit is quantised

(B)

The electron in the orbit nearest the nucleus has the lowest energy

(C)

Electrons revolve in different orbits around the nucleus

(D)

The position and velocity of the electrons in he orbit cannot be determined timultaneously

Solution:

Concept of electrons move in a circular path of fixed energy called orbits was put
forward by Bohr and not derived from Rutherford's scattering experiment.
Out of a large number of circular orbits theoretically possible around the nucleus, the
electron revolve only in those orbits which have a tired value of energy. Hence, these
orbits are called energy level or stationary states
Correct Answer is `=>` (D) The position and velocity of the electrons in he orbit cannot be determined timultaneously
Q 2827067881

Who modified Bohr's theory by introducing eliptical orbits for electron path?

(A)

Hund

(B)

Thomson

(C)

Somrnerfeld

(D)

Rutherford

Solution:

Concept of electrons move in a circular path of fixed energy called orbits was put
forward by Bohr and not derived from Rutherford's scattering experiment.
Out of a large number of circular orbits theoretically possible around the nucleus, the
electron revolve only in those orbits which have a tired value of energy. Hence, these
orbits are called energy level or stationary states
Correct Answer is `=>` (C) Somrnerfeld
Q 2827767681

When a electron moves from a higher orbit to the lower orbit then

(A)

emission of energy takes place

(B)

the size of atom increases

(C)

absorption of energy takes place

(D)

an electron in an atom moves without emission or absorption

Solution:

Concept of electrons move in a circular path of fixed energy called orbits was put
forward by Bohr and not derived from Rutherford's scattering experiment.
Out of a large number of circular orbits theoretically possible around the nucleus, the
electron revolve only in those orbits which have a tired value of energy. Hence, these
orbits are called energy level or stationary states
Correct Answer is `=>` (A) emission of energy takes place

Electromagnetic Radiation and Plank’s Quantum Theory

Q 1916767670

Arrange the following type of radiations in
increasing order of frequency:
(a) radiation from microwave oven
(b) amber light from traffic signal
(c) radiation from FM radio
(d) cosmic rays from outer space and
(e) X-rays.
Class 11 Exercise 2 Q.No. 45
Solution:

Cosmic rays > X-rays > amber colour > microwave> FM
Q 2887667587

The relation between energy of a radiation and its frequency was given by

(A)

Bohr's

(B)

de-Broglie

(C)

Rutherforcl

(D)

Planck's

Solution:

Cosmic rays > X-rays > amber colour > microwave> FM
Correct Answer is `=>` (D) Planck's
Q 2077678586

Match the following.







Column IColumn II
(A) X-rays (1) `v = 10^0 -10^4` Hz
(B) Ultraviolet wave (UV) (2) `v =10^10` Hz
(C) Long radio waves (3) `v =10^16` Hz
(D) Microwave (4) `v=10^18` Hz

NCERT Exemplar
Solution:

`A.-> (4) 8.->(3) C.->(1) D.->(2)`








Name FrequencyUses
(A) X-rays (1) `2 xx 10^16 -3 xx 10^19` Hz Medical pictures, material testing
(B) Ultraviolet wave (UV) (1) `7.9xx10^14 -2xx10^16` Hz Germisidal lamp
(C) Long radio waves (1) `10^0- 10 ^4` Hz Medical pictures, material testing
(D) Microwave (1) `1 xx 10^9 - 5 xx 10^11 ` Hz Cooking radar
Q 2837767682

The value of Planck's constant is

(A)

`6.6xx10^(-32) g//m^2 s`

(B)

`6.6xx10^(-34) kgm^2//s`

(C)

`6.6xx10^(-33) kg//ms^(-1)`

(D)

`6.6xx10^(-34) gs^(-1)`

Solution:

`A.-> (4) 8.->(3) C.->(1) D.->(2)`








Name FrequencyUses
(A) X-rays (1) `2 xx 10^16 -3 xx 10^19` Hz Medical pictures, material testing
(B) Ultraviolet wave (UV) (1) `7.9xx10^14 -2xx10^16` Hz Germisidal lamp
(C) Long radio waves (1) `10^0- 10 ^4` Hz Medical pictures, material testing
(D) Microwave (1) `1 xx 10^9 - 5 xx 10^11 ` Hz Cooking radar
Correct Answer is `=>` (B) `6.6xx10^(-34) kgm^2//s`

Atomic Number, Atomic Mass and Different Atomic Species

Q 1783267147

Identify the pairs which are not of isotopes?

NCERT Exemplar

(This question may have multiple correct answers)

(A) `text()_6^(12)X`, `text()_6^(13)Y`
(B) `text()_(17)^(35)X`, `text()_(17)^(37)Y`
(C) `text()_6^(14)X` ,`text()_7^(14)Y`
(D) `text()_4^8X`, `text()_5^8Y`
Solution:

(a) `text()_6^(12)X`, and `text()_6^(12)Y` have same atomic number but different mass number.

(b) `text()_(17)^(35)X` and `text()_(17)^(37)Y` have same atomic number but different mass number. Both these pairs are
isotopes to each other.


(c) `text()_6^(14)X` and `text()_7^(14)Y` have different atomic number but same mass number


(d) `text()_4^8X` and `text()_5^8Y` have different atomic number but same mass number.
Both these pairs are isobars to each other
Correct Answer is `=>` (C)
Q 2837667582

Which of the following properties of the element can be a whole number?

(A)

Atomic mass

(B)

atomic number

(C)

Atomic radius

(D)

Atomic volume

Solution:

atomic number
Correct Answer is `=>` (B) atomic number
Q 2817567489

The atomic number of an element of mass number 27, which has 13 neutron is

(A)

`10`

(B)

`14`

(C)

`12`

(D)

`13`

Solution:

atomic number
Correct Answer is `=>` (B) `14`
Q 1733667542

In which of the following pairs, the ions are iso electronic?

NCERT Exemplar
(A)

`Na^+ ,Mg^(2+)`

(B)

`Al^(3+),O^-`

(C)

`Na^+,O^(2-)`

(D)

`N^(3-),Cl^-`

Solution:

for ` Na^+ = 11-1 = 10 e^-`

`Mg^(2+) = 12-2 = 10 e^-`

Thus, they have same number of electrons

for `Al^(3+) = 13-3 = 10 e^- ,O^- = 8+1 = 9 e^-`

They do not have same number of electrons

for ` Na^+ = 10 e^- ,O^(2-) = 8+2 = 10 e^-`

They have same number of electrons

for `N^(3-) = 7+3 = 10 e^- , Cl^(-) = 17+1 = 18 e^-`

They do not have same number of electrons

Thus. `Na^+` is isoelectronic with `Mg^(2+)` and `O^(2-)`.
Correct Answer is `=>` (A)
Q 2857667584

Neutrons are present in all atoms except

(A)

He

(B)

C

(C)

H

(D)

N

Solution:

for ` Na^+ = 11-1 = 10 e^-`

`Mg^(2+) = 12-2 = 10 e^-`

Thus, they have same number of electrons

for `Al^(3+) = 13-3 = 10 e^- ,O^- = 8+1 = 9 e^-`

They do not have same number of electrons

for ` Na^+ = 10 e^- ,O^(2-) = 8+2 = 10 e^-`

They have same number of electrons

for `N^(3-) = 7+3 = 10 e^- , Cl^(-) = 17+1 = 18 e^-`

They do not have same number of electrons

Thus. `Na^+` is isoelectronic with `Mg^(2+)` and `O^(2-)`.
Correct Answer is `=>` (C) H
Q 2867667585

Which. one of the following pairs is correctly matched?

(A)

Mass spectrograph-Chadwick

(B)

Atomic number-Moseley

(C)

Neutron-Millikan's

(D)

Measurement of charge of an electron-Astron

Solution:

for ` Na^+ = 11-1 = 10 e^-`

`Mg^(2+) = 12-2 = 10 e^-`

Thus, they have same number of electrons

for `Al^(3+) = 13-3 = 10 e^- ,O^- = 8+1 = 9 e^-`

They do not have same number of electrons

for ` Na^+ = 10 e^- ,O^(2-) = 8+2 = 10 e^-`

They have same number of electrons

for `N^(3-) = 7+3 = 10 e^- , Cl^(-) = 17+1 = 18 e^-`

They do not have same number of electrons

Thus. `Na^+` is isoelectronic with `Mg^(2+)` and `O^(2-)`.
Correct Answer is `=>` (B) Atomic number-Moseley
Q 1713056840

Two atoms are said to be isobars if
NCERT Exemplar
(A)

they have same atomic number but different mass number

(B)

they have same number of electrons but different number of neutrons

(C)

they have same number of neutrons but different number of electrons

(D)

sum of the number of protons and neutrons is same but the number of protons is different

Solution:

Isobars have the same mass number (i.e., sum of protons and neutrons) but different
atomic number (i.e., number of protons). e.g., `text()_18 Ar^(40)` and `text()_19K^(40)` are isobars.
Correct Answer is `=>` (D) sum of the number of protons and neutrons is same but the number of protons is different
Q 2857767684

The number of neutrons in `text()_(13)Al^(27)` is

(A)

`40`

(B)

`27`

(C)

`14`

(D)

`13`

Solution:

Number of neutrons in `text()_(13)^(27)Al` is `14` (number of neutrons = mass number atomic number)
Correct Answer is `=>` (C) `14`
Q 2867767685

An element M has atomic mass 19 and atomic number 9. Its ion is represented ab

(A)

`M^+`

(B)

`M^(2+)`

(C)

`M^(-)`

(D)

`M^(2-)`

Solution:

`text()_(9)^(19)M = 1s^2 , 2s^2 , 2p^5` Its ion is represented by `M^-`
Correct Answer is `=>` (C) `M^(-)`
Q 1713167040

Chlorine exists in two isotopic forms. Cl-37 and Cl-35 but its atomic mass is 35.5. This indicates the ratio of Cl-37 and Cl-35 is approximately
NCERT Exemplar
(A)

1:2

(B)

1:1

(C)

1 :3

(D)

3 : 1

Solution:

The fractional atomic mass ( 35.5) of chlorine is clue to the fact that in ordinary chlorine
atom, Cl-37 and Cl-35 are present in the ratio of 1 : 3.


Average atomic mass of `Cl = (3xx35+1xx37)/4 = 35.5` amu
Correct Answer is `=>` (C) 1 :3
Q 2877767686

The number of electrons in `text()_(8)O^(16)` an isotope of oxygen is

(A)

`8`

(B)

`6`

(C)

`12`

(D)

`10`

Solution:

The fractional atomic mass ( 35.5) of chlorine is clue to the fact that in ordinary chlorine
atom, Cl-37 and Cl-35 are present in the ratio of 1 : 3.


Average atomic mass of `Cl = (3xx35+1xx37)/4 = 35.5` amu
Correct Answer is `=>` (A) `8`
Q 2887767687

Which one among the following most correctly determines the atomic number of an element

(A)

Number of protons

(B)

Number of protons and neutrons

(C)

Number of ions

(D)

Number of nucleons

Solution:

The fractional atomic mass ( 35.5) of chlorine is clue to the fact that in ordinary chlorine
atom, Cl-37 and Cl-35 are present in the ratio of 1 : 3.


Average atomic mass of `Cl = (3xx35+1xx37)/4 = 35.5` amu
Correct Answer is `=>` (A) Number of protons
Q 2817767689

Consider the following statements.in `text()_(38)^(90) Sr^(2+)`
I. Atomic number is `36`
II. Number of electrons is `38`.
III. Number of neutrons is `52.`
IV. Number of protons is 38.
Which of the above statements is/are correct?

(A)

I and II

(B)

II and Ill

(C)

III and IV

(D)

I and IV

Solution:

`text()_(38)^(92)Sr^(2+)` Atomic number `= 38`

= number of protons.
Number of electrons ` = 38-2 = 36`

Number of neutrons ` = 90-38 = 52`

Hence, statement III and IV are correct
Correct Answer is `=>` (C) III and IV
Q 2827867781

Consider the following statements in reference to the structure of atom.
I. lsotopes are the atoms of the same element having same atomic number but different mass-numbers.
II. Isobars are the atoms of different elements having different atomic number but same mass-number.
III. Isotones are atoms of different elements having same number of neutrons.
Which of the above statements is/are correct?

(A)

only I

(B)

only II

(C)

II and III

(D)

All of the above

Solution:

`text()_(38)^(92)Sr^(2+)` Atomic number `= 38`

= number of protons.
Number of electrons ` = 38-2 = 36`

Number of neutrons ` = 90-38 = 52`

Hence, statement III and IV are correct
Correct Answer is `=>` (D) All of the above
Q 2807867788

Which of the following statement is incorrect ?

(A)

Isobars possess same chemical properties

(B)

Isotopes occupy same position in periodic table

(C)

Isotopes possess same atomic number

(D)

In isobars the total number of protons and neutrons in the nucleus is same

Solution:

`text()_(38)^(92)Sr^(2+)` Atomic number `= 38`

= number of protons.
Number of electrons ` = 38-2 = 36`

Number of neutrons ` = 90-38 = 52`

Hence, statement III and IV are correct
Correct Answer is `=>` (A) Isobars possess same chemical properties
Q 2817867789

The number of protons in a negatively charged atom (anion) is

(A)

more than the atomic number of an element

(B)

less than the atomic number of an element

(C)

more than the number of electrons in the atom

(D)

less than the number of electrons in the atom

Solution:

`text()_(38)^(92)Sr^(2+)` Atomic number `= 38`

= number of protons.
Number of electrons ` = 38-2 = 36`

Number of neutrons ` = 90-38 = 52`

Hence, statement III and IV are correct
Correct Answer is `=>` (D) less than the number of electrons in the atom

Quantum Mechanical Model of Atom, Quantum Numbers and Electronic Configuration of Elements






Q 1703056848

Whch of the following is responsible to rule out the existence of
definite paths or trajectories of electrons?
NCERT Exemplar
(A)

Pauli's exclusion principle

(B)

Heisenberg's uncertainty principle

(C)

Hund's rule of maximum multiplicity

(D)

Aufbau principle

Solution:

Werner Heisenberg, a German physicist in 1927, stated uncertainty principle which
states that it is impossible to determine simultaneously, the exact position and exact
momentum of an electron.


Mathematically, = ` Deltax xxDeltapgeh/(4pi)`


The important implications of the Heisenberg uncertainty principle is that it rules out
existence of definite paths or trajectories of electrons and other similar particles.
Correct Answer is `=>` (B) Heisenberg's uncertainty principle
Q 2827667581

The atom of an element contains 2 electrons in its M shell. The element is

(A)

alurninium

(B)

sodium

(C)

chorine

(D)

magnesium

Solution:

Werner Heisenberg, a German physicist in 1927, stated uncertainty principle which
states that it is impossible to determine simultaneously, the exact position and exact
momentum of an electron.


Mathematically, = ` Deltax xxDeltapgeh/(4pi)`


The important implications of the Heisenberg uncertainty principle is that it rules out
existence of definite paths or trajectories of electrons and other similar particles.
Correct Answer is `=>` (D) magnesium
Q 1743167043

The pair of ions having same electronic configuration is ............
NCERT Exemplar
(A)

`Cr^(3+), Fe^(3+)`

(B)

`Fe^(3+) ,Mn^(2+)+`

(C)

`Fe^(3+), Co^(3+)`

(D)

`Sc^(3+), Cr^(3+)`

Solution:

`text()_24Cr = [Ar]3d^5, 4s^1` , `text()_24Cr^(3+) = [Ar]3d^3`


`text()_26Fe = [Ar]3d^6, 4s^2` , `text()_26Fe^(3+) = [Ar]3d^5`



`text()_25Mn = [Ar]3d^5, 4s^2` , `text()_25Mn^(2+) = [Ar]3d^5`



`text()_27Co = [Ar]3d^7, 4s^2` , `text()_27Co^(3+) = [Ar]3d^6`


`text()_21Sc = [Ar]3d^1, 4s^2` , `text()_21Sc^(3+) = [Ar]`


Thus, `Fe^(3+)` and `Mn^(2+)` have the same electronic configuration
Correct Answer is `=>` (B) `Fe^(3+) ,Mn^(2+)+`
Q 2837067882

Which of the following electronic configuration is not possible?

(A)

`1s^2`

(B)

`1s^2 , 2s^2 , 2p^6 , 3d^(10) , 3s^2`

(C)

`1s^2 , 2s^2 , 2p^6`

(D)

`1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 4s^1`

Solution:

`text()_24Cr = [Ar]3d^5, 4s^1` , `text()_24Cr^(3+) = [Ar]3d^3`


`text()_26Fe = [Ar]3d^6, 4s^2` , `text()_26Fe^(3+) = [Ar]3d^5`



`text()_25Mn = [Ar]3d^5, 4s^2` , `text()_25Mn^(2+) = [Ar]3d^5`



`text()_27Co = [Ar]3d^7, 4s^2` , `text()_27Co^(3+) = [Ar]3d^6`


`text()_21Sc = [Ar]3d^1, 4s^2` , `text()_21Sc^(3+) = [Ar]`


Thus, `Fe^(3+)` and `Mn^(2+)` have the same electronic configuration
Correct Answer is `=>` (B) `1s^2 , 2s^2 , 2p^6 , 3d^(10) , 3s^2`
Q 1753156944

Total number of orbitals associated with third shell will be ...........
NCERT Exemplar
(A)

2

(B)

4

(C)

9

(D)

3

Solution:

Total number of orbitals associated with nth shell= `n^2`

Total number of orbitals associated with third shell= `(3)^2 = 9`
Correct Answer is `=>` (C) 9
Q 1783156947

Orbital angular momentum depends on .........
NCERT Exemplar
(A)

`l`

(B)

`n` and `l`

(C)

`n` and `m`

(D)

`m` and `s`

Solution:

Orbital angular momentum `mvr = h/(2pi)sqrt(l(l+1))`


Hence, it depends only on `'l '. l` can have values ranging from `0` to `(n - 1)`

(a) When `l = 0`, the subshell iss and orbital is spherical in shape.

(b) When `l = 1`, the subshell is pand orbital is dumb-bell shaped.

(c) When `l = 2`, the subshell is d and orbital is double dumb-bell shaped.

(d) When `l = 3`, the subshell is f and orbital is complicated in shape.
Correct Answer is `=>` (A) `l`
Q 2877067886

From amongst the following chemical species .
I. `text()_(18)Ar^(39)`
II. `text()_(19)^(40) K^+`
III. `text()_(20)^(40)Ca^(2+)`
IV. `text()_(20)^(40) Ca^(+)`
The species having identical electronic configuration are

(A)

I and II

(B)

II and Ill

(C)

III and IV

(D)

I , II and III

Solution:

`text()_(18)^(39)Ar , text()_(19)^(40)K^+ ` and `text()_(20)^(40) Ca^(2+)` are isoelectronic species, thus, all these have same eletronic configuration.
Correct Answer is `=>` (D) I , II and III
Q 2057578484

Match the Quantum numbers with the information provided by these.








Quantum number Information provided
(A) Principal quantum number (1) Orientation of the orbital
(B) Azimuthal quantum number (2) Energy and size of orbital
(C) Magnetic quantum number (3) Spin of electron
(D) Spin quantum number (4) Shape of the orbital

NCERT Exemplar
Solution:

`A.-> (2) B. -> (4) C. -> (1) D. -> (3)`

A. Principal quantum number is the most important quantum number as it determines the
size and to large extent the energy of the orbital.

B. Azimuthal quantum number determines the angular momentum of the electron and
defines the three-dimensional shape of the orbital.

C. Magnetic quantum number gives information about the spatial orientation of orbitals
with respect to a standard set of coordinate axes.

D. Spin quantum number arises from the spectral evidence that an electron in its motion
around the nucleus in an orbit also rotates or spin about its own axis.
Q 1743667543

Which of the following statements concerning the quantum numbers are correct?
NCERT Exemplar

(This question may have multiple correct answers)

(A) Angular quantum number determines the three dimensional shape of the orbital
(B) The principal quantum number determines the orientation and energy of the orbital
(C) Magnetic quantum number determines the size of the orbital
(D) Spin quantum number of an electron determines the orientation of the spin of electron relative to the chosen axis
Solution:

(a) Azimuthal quantum number 'l' is also known as orbital angular momentum or
subsidiary quantum number. It determines three dimensional shape of the orbital.

(b) The principal quantum number determines the size of the orbit.

(c) Magnetic quantum number determines the orientation of the electron cloud in a
subshell.

(d) An electron spins around its own axis, much in a similar way as earth spins around its
own axis while revolving around the sun. In other words, an electron has. besides
charge and mass. intrinsic spin angular quantum number.
Correct Answer is `=>` (A)
Q 2847067883

The rule which states that no two eleetrons can have same value of all the four quantum numbers is

(A)

Pauli's exclusion principle

(B)

Heisenberg's uncertainty principle

(C)

Aufbau principle

(D)

de-Broglie principle

Solution:

(a) Azimuthal quantum number 'l' is also known as orbital angular momentum or
subsidiary quantum number. It determines three dimensional shape of the orbital.

(b) The principal quantum number determines the size of the orbit.

(c) Magnetic quantum number determines the orientation of the electron cloud in a
subshell.

(d) An electron spins around its own axis, much in a similar way as earth spins around its
own axis while revolving around the sun. In other words, an electron has. besides
charge and mass. intrinsic spin angular quantum number.
Correct Answer is `=>` (A) Pauli's exclusion principle
Q 2867067885

The electronic configuration of chromium ( Z = 24)` is

(A)

`1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^4 , 4s^2`

(B)

`1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^5 , 4s^1`

(C)

`1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 4s^2 , 4p^4`

(D)

`1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^6`

Solution:

`text()_(24)Cr = 1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^5 , 4s^1`
Correct Answer is `=>` (B) `1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^5 , 4s^1`
Q 2857167984

Match the following.






Column I (Electronic configuration) Column II (Elements)
(A) `1s^2` (1) Chlorine
(B) `1s^2 , 2s^2 , 2p^6` (2) Fluoride ion
(C) `1s^2 , 2s^2 , 2p^6 , 3s^2` (3) Hydride ion
(D) `1s^2 , 2s^2 , 2p^6 , 3s^2, 3p^5` (4) Magnesium


(A)

`A → 3 , B → 2 , C → 4 , D → 1`

(B)

`A → 3 , B → 4 , C → 2 , D → 1`

(C)

`A → 4 , B → 2 , C → 1 , D → 3`

(D)

`A → 2 , B → 3 , C → 4 , D → 1`

Solution:

`text()_(24)Cr = 1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 3d^5 , 4s^1`
Correct Answer is `=>` (A) `A → 3 , B → 2 , C → 4 , D → 1`
Q 2087578487

Match the following rules with their statements.








Rules Statement
(A) Hund's Rule (1) No two electrons in an atom can have the same set
of four quantum numbers.
(B) Aufbau Principle (2) Half-filled and completely filled orbitals have extra
stability.
(C) Pauli Exclusion Principle (3) Pairing of electrons in the orbitals belonging to the
same subshell does not take place until each orbital is singly occupied.
(D) Heisenberg's Uncertainty Principle(4) It is impossible to determine the exact position and
exact momenturn of a subatomic particle simultaneously.
(5) In the ground state of atoms, orbitals are filled in the
order of their increasing energies

NCERT Exemplar
Solution:

`A.-> (3) B.-> (5) C.->(1) D.-> (4)`

A. Hund's rule states that pairing of electrons in the orbitals belonging to the same
subshell (p, d or f) does not take place until each orbital belonging to that subs hell has
got one electron each i.e., it is singly occupied.

B. Aufbau principle states that in the ground state of the atoms, the orbitals are filled in
order of their increasing energies.

C. According to Pauli exclusion principle, no two electrons in an atom can have the same
set of four quantum numbers.

D. Heisenberg's uncertainty principle states that it is impossible to determine the exact
position and exact momentum of a subatomic particle simultaneously.

Radioactivity and Stability of Nucleus

Q 2817067889

Protons and neutrons are bound in a nucleus by

(A)

short range 'weak interaction

(B)

short range 'strong interaction

(C)

long range 'electromagnetic interaction'

(D)

long range 'gravitational'

Solution:

`A.-> (3) B.-> (5) C.->(1) D.-> (4)`

A. Hund's rule states that pairing of electrons in the orbitals belonging to the same
subshell (p, d or f) does not take place until each orbital belonging to that subs hell has
got one electron each i.e., it is singly occupied.

B. Aufbau principle states that in the ground state of the atoms, the orbitals are filled in
order of their increasing energies.

C. According to Pauli exclusion principle, no two electrons in an atom can have the same
set of four quantum numbers.

D. Heisenberg's uncertainty principle states that it is impossible to determine the exact
position and exact momentum of a subatomic particle simultaneously.
Correct Answer is `=>` (B) short range 'strong interaction
Q 2827167981

Following questions consist of two statements labelled as Statement I and Statement II. Examine both the Statements carefully and mark the correct choice according to the codes given below.
Statement I :Among `C^(12),C^(13)` and `C^(14)` only `C^(14)` is radioactive.
Statement II : `The `n/p` ratio in `C^(14)` is higher.

(A)

Both the statements are true and Statement II is the correct explanation of Statement I

(B)

Both the statements are true but Statement II is not the correct explanation of Statement I.

(C)

Statement I is true, but Statement II is false

(D)

Statement I is false, but Statement II is true.

Solution:

`A.-> (3) B.-> (5) C.->(1) D.-> (4)`

A. Hund's rule states that pairing of electrons in the orbitals belonging to the same
subshell (p, d or f) does not take place until each orbital belonging to that subs hell has
got one electron each i.e., it is singly occupied.

B. Aufbau principle states that in the ground state of the atoms, the orbitals are filled in
order of their increasing energies.

C. According to Pauli exclusion principle, no two electrons in an atom can have the same
set of four quantum numbers.

D. Heisenberg's uncertainty principle states that it is impossible to determine the exact
position and exact momentum of a subatomic particle simultaneously.
Correct Answer is `=>` (A) Both the statements are true and Statement II is the correct explanation of Statement I
Q 2807067888

A stable nucleus (light with A < 10) has

(A)

exactly the same number of neutrons and protons

(B)

more neutrons that protons

(C)

no neutrons

(D)

no protons

Solution:

A stable nucleus has exactly the same number of neutrons and protons. The maximum stability is attained when `n/p = 1`
Correct Answer is `=>` (A) exactly the same number of neutrons and protons

Nature of Radiation, Group Displacement Law and Half-life Period

Q 2827167981

Following questions consist of two statements labelled as Statement I and Statement II. Examine both the Statements carefully and mark the correct choice according to the codes given below.
Statement I :Gamma rays are more penetrating than X-rays.
Statement II : Gamma rays have wavelengths that an smaller than those of X rays.

(A)

Both the statements are true and Statement II is the correct explanation of Statement I

(B)

Both the statements are true but Statement II is not the correct explanation of Statement I.

(C)

Statement I is true, but Statement II is false

(D)

Statement I is false, but Statement II is true.

Solution:

A stable nucleus has exactly the same number of neutrons and protons. The maximum stability is attained when `n/p = 1`
Correct Answer is `=>` (A) Both the statements are true and Statement II is the correct explanation of Statement I
Q 1642601533

If the half-life period of a first order reaction is `138.6\ min`, then the value of decay constant for the reaction will be
MHCET 2013
(A)

`5\ min^-1`

(B)

`0.5\ min^-1`

(C)

`0.05\ min^-1`

(D)

`0.005\ min^-1`

Solution:

Rate constant for the first order reaction =` \frac{0.693}text{ half life} = \frac{0.693}{t_{1/2}}`

`K = \frac{0.693}{t_{1/2}} = \frac{0.693}{138.6} = 0.005\ min^{-1} `
Correct Answer is `=>` (D) `0.005\ min^-1`
Q 1641012823

Calculate the rate constant for the radioactive
disintegration of an isotope that has a half-life
of `6930` yr.
GGSIPU 2015
(A)

`1.00 xx 10^-5 yr^-1`

(B)

`1.00 xx 10^(-4) yr^(-1)`

(C)

`1.00 xx 10^(-3) yr^(-1)`

(D)

`1.00 xx 10^-3 yr^-1`

Solution:

Half-life of an isotope; `t_(1/2) = 6930` yr.

`t_(1/2) = 0.693/k`

`k= 0.693/ t_(1/2)`
`k =0.693/ 6930 yr^(-1)`

`= 1 xx 10^(-4) yr^(-1)`
Correct Answer is `=>` (B) `1.00 xx 10^(-4) yr^(-1)`

Nuclear Fission and Nuclear Fusion

Q 1773445346

Which material is used as a neutron moderator?
AIIMS 2011
(A)

Graphite

(B)

Cadmium

(C)

Boron

(D)

Uranium

Solution:

Neutron moderators slow down the speed of neutrons by collisions. They do not absorb neutron. e.g. water and graphite.
Correct Answer is `=>` (A) Graphite
 
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