mol of $O_2=\large\frac{6}{32}$

$\therefore $ No of molecules in $\large\frac{6}{32}$ moles of $O_2=\large\frac{6}{32} $$\times 6.022 \times 10^{23}$

Mol of $SO_2=\large\frac{6}{64} $ and number of molecules of

$SO_2=\large\frac{6}{64} $$\times 6.022 \times 10^{23}$

Thus number of molecules of $SO_2$ will be less than that of $O_2$

Hence c is the correct answer.