Q-what is the  HNH bond angle in NH3?

Ans-In NH3 (ammonia )there are 4 bond pair and 1lone pair, and due to VSPER theory lone pair -bond pair repulsion is > bond pair- bond pair repulsion.

lp-lp>lp-bp>bp-bp

So the lone pair electrons present on N atom repeal N-H pair of electrons. So bond angle between HNH contract and it is about 107°.