A 4 : 1 molar mixture of He and CH₄ is contained in a vessel at 20 bar pressure. Due to a hole in the vessel the gas mixture leaks out. What is the composition of the mixture effusing out initially?

An LPG (liquefied petroleum gas) cylinder weighs 14.8 kg when empty. When full, it weighs 29.0 kg and shows a pressure of 2.5 atm. In the course of use at 27^o C, the weight of the full cylinder reduces to 23.2 kg. Find out the volume of the gas in cubic meters used up at the normal usage conditions find the final pressure inside the cylinder. Assume LPG to be n-butane with normal boiling point of 0^o C.

Complete and balance the following reactions:
Ca₅(PO₄)₃F + H₂SO₄ + H₂O $$\buildrel {Heat} \over \longrightarrow $$ ........ + 5CaSO₄.2H₂O + ........

Statement (S) The alkali metals can form ionic hydrides which contain the hydride ion H^-.
Explanation (E) The alkali metals have low electronegativity; their hydrides conduct electricity when fused and liberate hydrogen at the anode.