An oxide XO2 has a vapour density of 32. What is the atomic mass of X?

A. 20
B. 32
C. 14
D. 12

Correct Answer:

Option B – 32

Explanation

Molecular mass = vapour density x 2

Mm of XO2 = x + 16(2) = x + 32

vapour density = 32

∴ x + 32 = 32 × 2

x + 32 = 64

x = 64 – 32

x = 32

∴ the relative molecular mass of X is 32
Relative molecular mass = vapour density × 2