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### Question Asked by a Student from EXXAMM.com Team

** Q 2660012815. ** (a) You are given marbles of diameter 10 mm. They are to be placed such that their centres are lying in a square bound by four lines each of length 40 mm. What will be the arrangements of marbles in a plane so that maximum number of marbles can be placed inside the area? Find the maximum number of marbles per unit area and derive the expression for calculating it.

(b) 1 g of charcoal adsorbs 100 ml 0.5 M `CH_3COOH` to form a monolayer, and thereby the concentration of `CH_3COOH`

reduces to 0.49 M. Calculate the surface area of charcoal occupied by each molecule of acetic acid. Given that surface area of charcoal `= 3.01 xx 10^2` `m^2//g`.

**JEE 2003 Mains **