How many grams of MgCO3 contain 24.00 g of oxygen

How many grams of MgCO₃ contain 24.00 g of oxygen? (The molar mass of MgCO₃ is 84.30 g mol^–1)

1. 42.15 g
2. 84.30 g
3. 126.00 g
4. 154.00 g

Answer

Mass of oxygen atom = 16 g

Mass of oxygen in 84.30 g of MgCO₃ = 3 x 16 = 48 g

So, 24 g of oxygen will be in 42.15 g of MgCO₃.

The correct option is A.