Question

no of valence electron present in 6.4 g of O^2-

Answer 1

zero as no valence electrons are present in O2^2-

Answer 2

Answer: $19.3\times 10^{23}$ electrons.

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{6.4g}{16g/mol}=0.4moles$

Electronic configuration of oxygen:

$[O]:8:1s^22s^22p^4$

Valence electrons of oxygen =  6

$[O^{2-}]:10:1s^22s^22p^6$

Valence electrons of $O^{2-}$ = 8

1 mole of  $O^{2-}$ contains =$8\times 6.023\times 10^{23}=48.18\times 10^{23}$ electrons

0.4 moles of $O^{2-}$ contains =$\frac{48.18\times 10^{23}}{1}\times 0.4=19.3\times 10^{23}$ electrons

Thus total number of valence electrons in 6.4 g of $O^{2-}$ ion is $19.3\times 10^{23}$ electrons.