The number of atoms in 4.25g of NH₃ is approximately

The number of molecules in 4.25 g of NH₃  = $\frac{4.25\times 6.02\times {10}^{23}}{17}=0.25\times 6.02\times {10}^{23}$

Number of atoms in NH₃ = Atomicity $\times$number of molecules = 4 $\times$ 0.25 $\times$6.02 $\times$10²³ = 6.02 $\times$10²³