16 g of oxygen has same number of molecules as in

1.  16 g of CO

2.  28 g of N2

3.  14 g of N2

4.  1.0 g of H2

(c, d)
The number of molecules can be calculated as follows
Number of molecules=MassMolar mass×Avogadro number (NA)
Number of molecules, in 16 g oxygen=1632×NA=NA2
In 16 g of CO=1628×NA=NA1.75
In 28 g of N2=2828×NA=NA
In 14 g of N2=1428×NA=NA2
In 1 g of H2=12×NA=NA2
So, 16 g of O2=14 g of N2=1.0 g of H2