Number of atoms in 4.25 g of $N{H}_3$ is:

The correct option is A $6.023\times {10}^{23}$

Atomic mass of $N=14u$

Atomic mass of $H=1u$

Molar mass of $N{H}_3=14+3=17g/mol$

No.of moles $=\frac{4.25}{17}=0.25$ moles

Number of molecules in 4.2 g $N{H}_3=0.25\times 6.022\times {10}^{23}$

Number of atoms in one molecule of $N{H}_3=4$

Number of atoms in 4.2 g $N{H}_3=4\times 0.25\times 6.022\times {10}^{23}$ = $6.022\times {10}^{23}$