Explanation

(c) $s = ut + \frac{1}{2}\ at^{2}$
For Ist body
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ u = 0\ \ and\ \ a = g\ \ \ \ \ \ \ \lbrack freely\ falling\ body\rbrack$
Distance covered in 2 s,
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s_{1} = 0 + \frac{1}{2}\ g\ (3)^{2}$
For IInd body
Distance covered in 2 s,
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s_{2} = 0 + \frac{1}{2}g(2)^{2}$
$\therefore\ \ s_{1} - s_{2} = \frac{1}{2}g\left\lbrack (3)^{2} - (2)^{2} \right\rbrack$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{1}{2}g(9 - 4) = 25\ m$