Explanation

(c)
No. of atoms in 1g of $O_{2}(g) = 2 \times \frac{1}{32} \times 6.023 \times 10^{23}$
$= 0.38 \times 10^{23}$
No. of atoms in 1g of $Ni(s) = \frac{1}{58.2} \times 6.023 \times 10^{23}$
$= 0.10 \times 10^{23}$
No. of atoms in 1g of $B(s) = \frac{1}{10.8} \times 6.023 \times 10^{23}$
$= 0.58 \times 10^{23}$
No. of atoms in 1g of $N_{2}(g) = 2 \times \frac{1}{28} \times 6.023 \times 10^{23}$
$= 0.43 \times 10^{23}$
Alternative: Smaller the atomic mass, larger will be the no. of atoms in sample.