If 150 cc of a gas A contains X molecules, how many molecules of gas B will be present in 75 cc of B. The gases A and B are under the same conditions of temperature and pressure. Name the law on which the problem is based.

Find the relative molecular mass of a gas, 0.546 g of which occupies 360 cm³ at 87°C and 380 mm Hg pressure. (1 litre of hydrogen at s.t.p. weighs 0.09 g)

2KMnO₄ ⟶ K₂MnO₄ + MnO₂ + O₂

K₂MnO₄ + MnO₂ is the solid residue.

Potassium permanganate was heated in a test tube. After collecting one litre of oxygen at room temperature, it was found that the test tube had undergone a loss in mass of 1.32 g. If one litre of H₂ under the same conditions of temperature and pressure has a mass of 0.0825 g. Calculate the relative molecular mass of oxygen.

A gas cylinder of capacity of 20 dm³ is filled with gas X the mass of which is 10 g. When the same cylinder is filled with hydrogen gas at the same temperature and pressure the mass of the hydrogen is 2 g, hence the relative molecular mass of the gas is :

1. 5
2. 10
3. 15
4. 20