8gm of sulphur is completely burnt to get sulphur dioxide.  The number of molecules of  $S{O}_2$ obtained is

64gms of  $S{O}_2$ contains 32gms of ‘S’ and ‘N’ molecules of  ‘S’.

$\therefore$ 8 gms of sulphur contains $\frac{8\times N}{32}$ molecules $=\frac{6\times {10}^{23}}{4}=1.5\times {10}^{23}$ molecules