1- mole of any Substance will have the same number of Molecules.
Molecular weight of CO2= 44
Molecular weight of H20= 18
So 18 g of H20 will contain the same Number of molecules as in 44 g of CO2.
Therefore 7.2 g of H2O will have same Number of Moleculesas in =7.2/18 x 44
= 17.6 g of CO2.