Answer : The angle between two of the nitrogen-hydrogen bonds in the ammonium ion
is,

Explanation :
Formula used :
![\text{Number of electrons}=(1)/(2)[V+N-C+A]](https://img.qammunity.org/2019/formulas/chemistry/middle-school/9092ozegyo6owf6gbmfgnwh1y8xvwkxj9r.png)
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
First we have to determine the hybridization of the
molecules.
![\text{Number of electrons}=(1)/(2)* [5+4-1]=4](https://img.qammunity.org/2019/formulas/chemistry/high-school/yjjshl60lbchcdf9xanjwtvajj7iy2o869.png)
The number of electrons are 4 that means the hybridization will be
and the electronic geometry of the molecule will be tetrahedral and the bond angle will be,
.
Hence, the angle between two of the nitrogen-hydrogen bonds in the ammonium ion
is,
