Explanation

(c)
$s$-character$\ \propto \$bond angle
For 25% $s$ character (as in $sp^{3}$hybrid orbital), bond angle is 109.$5{^\circ}$, for 33.3% $s$ character (as in $sp^{2}$ hybrid orbital),bond angle is $120{^\circ}$ and for 50% $s$ character (as in $sp$ hybrid orbital ), bond angle is $180{^\circ}$.
Similarly, when the bond angle decreases below $1.9.5{^\circ},$the$s -$character will decrease accordingly
Decreasing in angle $= 120{^\circ} - 109.5{^\circ} = 10.5$°
$\therefore$ Decrease in $s$-character $= 33.3 - 25 = 8.3$
Actual decrease in bond angle $= 109.5{^\circ} - 105{^\circ} = 4.5{^\circ}$
$\therefore$ Expected decrease in $s$-character
$= \frac{8.3}{10.5} \times 4.5 = 3.56\%$
Thus, the $s$-character should decrease by about 3.56%, $ie,\ s$-character $= 25 - 3.56 = 21.44\%$