Question

Why the bond angle in ammonia decrease the actual?

Answer 1

In ammonia there are N--H bonds

We know that Covalent bonds are formed by the sharing of electrons the shared pair of electrons between N----H are more attracted towards N due to its higher electronegativity

Due to the accumulation of the ELECTRONS near the single nitrogen atom it's bond angle decreases

I know that it is a little difficult to imagine

I hope this helps (θ‿θ)