Question

If NA is the Avogadro's number then number of valence electrons in 4.2g of nitride ion(N3−) is

Answer 1

Hope this will help u

Answer 2

Answer: $2.4\times N_A$

Explanation:

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}$

$Moles=\frac{4.2g}{14g/mol}=0.3moles$  

According to avogadro's law, 1 mole of every substance weighs equal to the molecular mass and contains avogadro's number $6.023\times 10^{23}$ of particles.

$N:7:1s^22s^22p^3$

$N^{3-}:10:1s^22s^22p^6$

Thus valence electrons are 2+6= 8.

1 mole of $N^{3-}$ has valence electrons =$8\times N_A$

0.3 moles of $N^{3-}$ has valence electrons =$\frac{8\times N_A}{1}\times 0.3=2.4\times N_A$