In the lewis dot structure for nh3, the central atom of the molecule has three atoms bonded to it and one lone pair of electrons. the shape of an nh3 molecule is bent.
tetrahedral.
trigonal planar.
trigonal pyramidal.

Answer : The correct option is, trigonal pyramidal.

Explanation :

Formula used  :

where,

V = number of valence electrons present in central atom

N = number of monovalent atoms bonded to central atom

C = charge of cation

A = charge of anion

Now we have to determine the hybridization of  molecule.

The number of electrons is 4 that means the hybridization will be and the electronic geometry of the molecule will be tetrahedral.

But as there are three atoms around the central nitrogen, the fourth position will be occupied by lone pair of electrons. The repulsion between lone and bond pair of electrons is more and hence the molecular geometry or shape will be trigonal pyramidal and the bond angle will be,

Hence, the shape of an ammonia molecule is, trigonal pyramidal.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)