Number of moles $ \frac{\text{wt}\text{.}\,\text{of}\,\text{substance}\,\text{in}\,\text{grams}}{\text{gram}\,\text{molecular}\,\text{wt}\text{.}} $ With the help of above formula we calculate number of moles for all the cases. It comes highest for 64 g of
$ S{{O}_{2}} $ as, Mol. wt. of $ S{{O}_{2}}=32+32=64\text{ }g $
Gram mol. wt. = 64 g
$ \therefore $ 64 g or 1 mol of $ S{{O}_{2}} $ contains $ =6.023\times {{10}^{23}} $ molecules