Which of the following contains maximum number of molecules?

For a fixed mass of gas, the number of molecules present equals the number of moles multiplied by Avogadro's number, and the number of moles is mass divided by molar mass. So for the same mass, the number of molecules is inversely proportional to molar mass — a lighter gas contains more molecules per gram than a heavier one.

Comparing 1 g of each gas given in the options:

1. Molar masses: H₂ = 2 g/mol, CH₄ = 16 g/mol, N₂ = 28 g/mol, CO₂ = 44 g/mol.

2. Moles in 1 g of each gas (moles = mass ÷ molar mass): H₂ gives 1/2 = 0.5 mol; CH₄ gives 1/16 = 0.0625 mol; N₂ gives 1/28 ≈ 0.036 mol; CO₂ gives 1/44 ≈ 0.023 mol.

3. Since the number of molecules equals moles multiplied by the same Avogadro's number for every sample, the gas with the greatest mole count has the greatest number of molecules.

4. Among 0.5, 0.0625, 0.036, and 0.023 mol, 0.5 mol is the largest, so 1 g H₂ gives the maximum number of molecules.

Independently: since every option uses the same 1 g mass, the molecule count is governed purely by molar mass, and H₂ has the smallest molar mass of the four gases — so it must yield the largest mole count. This confirms 1 g H₂ contains the maximum number of molecules.