Why is `BF_3` planar molecule but `NH_3` is pyramidal?

The BCl_3 is a planar molecule whereas NCl_3 is pyramidal because

In the following question, an Assertion (A) is followed by a corresponding Reason (R). Use the following keys to choose the appropriate answer. Assertion : BF_3 molecule is planar but NF_3 is pyramidal. Reason : N atom is smaller than B.

Which is a square planar molecule?

Account for the following: BF_3 is planar but NH_3 is not.

Which of the following is untrue regarding BF_3 ? It is a Lewis acid , It is a planar molecule, It has a dipole moment, It forms a compound with NH_3

What happens when BF_3 reacted with NH_3

Why does BF_3' act as a lewis acid?

Water molecule has a V-shape or bent structure and NH_3 molecule has pyramidal shape both has 4 electron pairs around the central atom. Justify the statement.