What mass of oxygen reacts with 3.6 g of magnesium to form magnesium oxide?

Answer is: the mass of the oxygen is 2.37 grams.

Balanced chemical reaction: 2Mg + O₂ → 2MgO.

m (Mg) = 3.6 g; mass of magnesium.

n (Mg) = m (Mg) : M (Mg).

n (Mg) = 3.6 g : 24.3 g/mol

n (Mg) = 0.149 mol.; amount of the magnesium.

n (O₂) = ?

From chemical reaction: n (Mg) : n (O₂) = 2 : 1.

n (O₂) = n (Mg) : 2.

n (O₂) = 0.149mol : 2.

n (O₂) = 0.075 mol; amount of the oxygen.

m (O₂) = m (O₂) · M (O₂).

m (O₂) = 0.075 mol · 32 g/mol.

m (O₂) = 2.37 g; mass of the oxygen.