Number of moles in 128 g of SO₂ will be

Concept: The number of moles of a substance is found using the mole-mass relationship — Number of moles (n) = Given Mass / Molar Mass (M) — where the molar mass of a compound equals the sum of the atomic masses of all the atoms present in one molecule of that compound.

1. One molecule of SO₂ contains one sulphur (S) atom and two oxygen (O) atoms. Using the standard atomic masses, S = 32 u and O = 16 u.

2. Molar mass of SO₂ = (1 × 32) + (2 × 16) = 32 + 32 = 64 g/mol.

3. Applying the formula, Number of moles = Given mass / Molar mass = 128 g / 64 g/mol = 2 mole.

Cross-check: If 1 mole of SO₂ weighs 64 g, then 2 mole of SO₂ should weigh 2 × 64 = 128 g, which is exactly the mass given in the question — confirming that 2 mole is correct.