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=MassMolarmass×Avogadronumber(NA)
Number of molecules, in 16 g oxygen=1632×NA=NA2
In16gofCO=1628×NA=NA1.75
In28gofN2=2828×NA=NA
In14gofN2=1428×NA=NA2
In1gofH2=12×NA=NA2
So, 16gofO2=14gofN2=1.0gofH2