Answer: Bond angle for methane is 109.5°,Bond angle for ammonia is 107° and Bond angle for water is 104.5°

: Formula used :{text{Number of electrons}} =frac{1}{2}[V+N-C+A]

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

a. Methane:CH_4

In the given molecule, carbon is the central atom and there are 4 Hydrogens as monovalent atoms.

Formula used :{text{Number of electrons}} =frac{1}{2}[4+4-0+0]=4

The number of electrons is 4 that means the hybridization will be sp^3 and geometry of the molecule will be tetrahedral.The bond angle for terahedral geometry is 109.5°.

b. Ammonia:NH_3

In the given molecule, nitrogen is the central atom and there are 3 Hydrogens as monovalent atoms.

Formula used :{text{Number of electrons}} =frac{1}{2}[5+3-0+0]=4

The number of electrons is 4 that means the hybridization will be sp^3 and geometry of the molecule will be pyramidal as there are three bond pairs and one lone pair.The bond angle for pyramidal geometry is 107°.the bond angle reduces due to lone pair bond pair repulsions.

c. water :H_2O

In the given molecule, oxygen is the central atom and there are 2 Hydrogens as monovalent atoms.

Formula used :{text{Number of electrons}} =frac{1}{2}[6+2-0+0]=4

The number of electrons is 4 that means the hybridization will be sp^3 and geometry of the molecule will be bent as there are two bond pairs and two lone pairs.The bond angle for pyramidal geometry is 104.5°.The bond angle reduces further due to greater lone pair-lone pair repulsions.