\[(a)\;2 \quad (b)\;1 \quad (c)\;5 \quad (d)\;3\]

Let $'h'$ be height of each storey of building using $ s=ut+\large\frac{1}{2}$$at^2$

$25h=0 \times 5 +\large\frac{1}{2}$$ \times 9.8 \times 5^2$

$\quad h=4.9m/s$

Distance covered in 1st second

$s_n=u+g\bigg(n-\large\frac{1}{2}$$\bigg)$

$\quad=0+9.8\bigg(1-\large\frac{1}{2}$$\bigg)$

= 4.9

Therefore it covers 1 storey in 1st second

Hence b is the correct answer.

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