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.