An oxide of M (MO) reacts completely with carbon to give 12.4g of metal M and 4.29g of carbon dioxide .what is the relative atomic mass of M?

Let y be the relative atomic mass of M.

2MO + C → 2M + CO₂

Mole ratio M : CO2 = (12.4/y) : [4.29/(12 + 16×2)] = 2 : 1
12.4/y = (4.29/44) × 2
y/12.4 = 22/4.29
y = 63.6

Relative atomic mass of M = 63.6