A white carbonate P of a period 2 metal imparts a crimson red colour to a flame. On strong heating P gives a gas that turns lime water milky and a solid Q that dissolves in water to give a sparingly soluble base. Using Li 7, C 12, O 16, the mass of Q obtained from 3.70 g of P is

Answer: A

A crimson flame and a period 2 alkali metal identify P as

Li X_{2} CO X_{3}

(M = 74).

Li X_{2} CO X_{3} Li X_{2} O + CO X_{2}

, and 3.70 g is 0.050 mol, giving 0.050 mol of

Li X_{2} O

(M = 30), i.e.

0.050 \times 30 = 1.50