Compound in which maximum percentage of s-character in $\mathrm{M}-\mathrm{H}$ bond is :

$\mathrm{P}-\mathrm{H}, \mathrm{H}-\mathrm{S}$ have almost pure p-character.
$\mathrm{N}-\mathrm{H} vs\mathit{ }\mathrm{O}-\mathrm{H}$

Ammonia has most number of s character in $\mathrm{M}-\mathrm{H}$ bond. 
Hence correct option is C.