Question

Number of neutrons present in $1.7\text{g}$ of ammonia is:

• A. $N_A$
• B. $\frac{N_A}{10\times 4}$
• C. $\left(N_A/10\right)\times 7$
• D. $N_A\times 10\times 7$

Answer 1

The correct option is C $\left(N_A/10\right)\times 7$

Given,
Mass of ammonia$=1.7\text{g}$
Molar mass of ammonia $=17{\text{g mol}}^{-1}$
Number of moles of ammonia$=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{1.7}{17}=0.1\text{mol}$
Hydrogen i.e., $H$ has no neutron.
One molecule of $N{H}_3$ contains $7$ neutrons
One mole of $N{H}_3$ contains $7N_A$ neutrons
Number of neutrons in $0.1\text{mol}$ of $N{H}_3=7\times 0.1N_A=0.7N_A=\left(N_A/10\right)\times 7$