Answer:
3
Explanation:
Put a 1 in front of the most complicated-looking formula [Fe₂(SO₄)₃]:
Fe₂O₃ + H₂SO₄ ⟶ 1Fe₂(SO₄)₃+ H₂O
Balance Fe:
Put a 1 in front of Fe₂O₃.
1Fe₂O₃ + H₂SO₄ ⟶ 1Fe₂(SO₄)₃+ H₂O
Balance S:
Put a 3 in front of H₂SO₄.
1Fe₂O₃ + 3H₂SO₄ ⟶ 1Fe₂(SO₄)₃+ H₂O
Balance O.
We have fixed 15 O on the left but only 12 O on the right. Put a 3 in front of H₂O.
1Fe₂O₃ + 3H₂SO₄ ⟶ 1Fe₂(SO₄)₃+ 3H₂O
Every formula now has a coefficient. The equation should be balanced.
Check:
Atom On the left On the right
Fe 2 2
O 15 15
H 6 6
S 3 3
The balanced equation is
Fe₂O₃ + 3H₂SO₄ ⟶ Fe₂(SO₄)₃+ 3H₂O
The coefficient of H₂O is 3.