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Q.
The total number of electrons in $4.2\, g$ of $N ^{3-}$ ion is $\left( N _{ A }\right.$ is the Avogadro's number)
Some Basic Concepts of Chemistry
Solution:
Total number of moles $=\frac{4.2}{14}=0.3\, mol$
$1\, mol$ of $N ^{3-}$ have electrons $=10 \times N _{0}$
$\therefore $ Number of $e ^{-}$ in $0.3\, mol$
$=0.3 \times 10 \times N _{0}=3 \times N _{0}$