the total no. of valence electrons in 4.2g of N3- ion is ??in terms of Na(Na is the avogadro no._)

Number of moles of nitride ions in 4.2 g = 4.2/14

  = 0.3 moles

Therefore, number of nitride ions in 0.3 moles = 0.3 x N_a

Number of valence electrons in one nitride ion = 8

So, number of valence electrons in 0.3 x N_a nitride ions = 8 x 0.3 x N_a

  = 2.4 x N_a