If 1 gram of sulphur dioxide contains x molecules, how many molecules will be present in 1 gram of oxygen ?
(S = 32 u ; O = 16 u)

Given:
Mass of sulphur dioxide = 1g
We know that equal moles of all substances contain equal number of molecules. (1 mole of all substances contains 6.022 × 10²³ molecules).
Therefore, the ratio of molecules in sulphur dioxide and oxygen will be same as the ratio of their moles.
Number of moles in 1g of sulphur dioxide:
1 mole of SO₂ = (1 × 32) + (2 × 16) = 64g
64g of SO₂ = 1 mole of SO₂
Therefore, 1g of SO₂ = 1/64 moles of SO₂
Now, 1/64 moles of SO₂ contain x molecules (given). Since equal number of molecules are present in equal moles of all substances, 1/64 moles of oxygen will also contain x number of molecules.
Number of moles in 1g of oxygen:
1 mole of O₂ = 2 × 16 = 32g
32g of O2 = 1 mole of O₂
Therefore, 1g of O₂ = 1/32 moles of O₂
We have already stated that 1/64 moles of oxygen contain x molecules. Therefore,
1/32 mole of oxygen will contain = x × 64 / 32 = 2x
Hence, 1 gm of oxygen consists of 2x number of molecules.