Question

If $N_A$ is the Avogadro’s number, then the number of valence electrons in $4.2\text{g}$ of nitride ions $\left(N^{3-}\right)$ is:

• A. $4.2N_A$
• B. $2.4N_A$
• C. $1.6N_A$
• D. $3.2N_A$

Answer 1

Answer: (B)

Step 1:
Moles of nitride ion $\Rightarrow \frac{givenmass}{molarmass}$
$\Rightarrow \frac{4.2}{14}=0.3N_A$ nitride ions.

Step 2:
The number of valence electrons in an nitride ion $=8(5+3\text{due to the charge})$
The number of valence electrons in $4.2\text{g}$ of nitride ions $\Rightarrow 8\times 0.3N_A=2.4N_A$

Hence, option (C) is correct.