The number of molecules in 16.0g of oxygen is

The correct option is D $3.01\times {10}^{23}$

32 g or 1 mole of $O_2$ = $6.023\times {10}^{23}$
So, 16 g of $O_2$ = $\frac{6.023\times {10}^{23}\times 16}{32}$
= $3.01\times {10}^{23}$ molecules