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# If $N_A$ is the Avogadro's number then number of valence electrons in 4.2g of nitride ion($N^{3-})$ is

$\begin{array}{1 1}(a)\;2.4N_A&(b)\;4.2N_A \\(c)\;1.6N_A&(d)\;3.2N_A\end{array}$

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• Avogadro's law states that under conditions of constant temperature and pressure,equal volume of gases contains equal number of particles.Experimental investigations show that at one atmosphere pressure and a temperature at 273K (i.e at STP) one mole of any gas occupies a volume which is very close to 22.4litres.Therefore,the number of moles in any gas sample can be found by comparing its volume at STP with 22.4.The mole is the S.I.base unit for the amount of a chemical species.It is always associated with a chemical formula and refers to Avogadro's number($6.022\times 10^{23})$ of particles denoted by the formula.It is represented by the symbol $N_A$.It is the number of atoms present in one gram atom of an element or the number of molecules present in one gran molecule of the substance.
No of moles =$\large\frac{4.2}{14}$$=0.3$mol
$0.3mol=0.3\times N_A$ ions
$\Rightarrow 8\times 0.3\times N_A$ electrons
$\Rightarrow 2.4N_A$ electrons
Because each ion contains 5+3=8$e^-$
Hence (a) is the correct answer.
edited Sep 12, 2014 by pady_1