Hey there!
Mg(OH)₂ + H₂(SO₄) → Mg(SO₄) + H₂O
Balance O. (not including SO₄)
2 on the left, 1 on the right. Add a coefficient of 2 in front of H₂O.
Mg(OH)₂ + H₂(SO₄) → Mg(SO₄) + 2H₂O
Balance H.
4 on the left, 4 on the right. Already balanced.
Balance SO₄. (polyatomic ion)
1 on the left, 1 on the right. Already balanced.
Balance Mg.
1 on the left, 1 on the right. Already balanced.
Our final balanced equation:
Mg(OH)₂ + H₂(SO₄) → Mg(SO₄) + 2H₂O
So your answer is a. 1, 1, 1, 2.
Hope this helps!