The number of sulphur atoms present in $0.2$ mole of sodium thiosulphate is ( $N=$ Avogadro number)

Given, $0.2$ moles of ${Na}_2{ S}_2{O}_3$ (sodium thiosulphate)

1 mole of ${Na}_2{ S}_2{O}_3$ contains 2 moles of $S$.

So, $0.2$ moles of ${Na}_2{ S}_2{O}_3=0.2\times 2=0.4$

No. of moles of $S=0.4$

No. of atoms $=n$ (no. of moles) $\times N_A$ (Avogadro's no.)

$\Rightarrow 0.4\times N=0.4N$

Hence, option (C) is the correct answer.