16 g of oxygen has same number of molecules as in

The molar mass of oxygen is 32. Therefore, 32g of oxygen contains 6.023 x 10²³ molecules. 16g of oxygen contains x 6.023 x 10²³ = 0.5 x 6.023 x 10²³ molecules.

16g of CO contains x 6.023 x 10²³ = 0.57 x 6.023 x 10²³ molecules.

28g of N₂ contains x 6.023 x 10²³ = 6.023 x 10²³ molecules.

14g of N₂ contains x 6.023 x 10²³ = 0.5 x 6.023 x 10²³ molecules.

1.0g of H₂ contains x 6.023 x 10²³ = 0.5 x 6.023 x 10²³ molecules.

Hence oxygen has the same number of molecules as (iii) and (iv).