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`.