Answer:
1
Step-by-step explanation:
C + SnO₂ ⟶ Sn + CO₂
1. Pick the most complicated-looking formula (SnO₂?).
Put a 1 in front of it.
C + 1SnO₂ ⟶ Sn + CO₂
2. Balance Sn.
Done.
Put a 1 in front of CS₂.
C + 1SnO₂ ⟶ 1Sn + CO₂
3. Balance O.
We have fixed 2O on the left. We need 2O on the right.
Put a 1 in front of CO₂.
C + 1SnO₂ ⟶ 1Sn + 1CO₂
4. Balance C
We have fixed 1C on the right. We need 1C on the left.
Put a 1 in front of C.
1C + 1SnO₂ ⟶ 1Sn + 1CO₂
All species have a coefficient. The equation should now be balanced.
5. Check that all atoms are balanced
The balanced equation should have the same number of atoms on each side of the reaction arrow.

The balanced equation is
1C + SnO₂ ⟶ Sn +2CO₂
The coefficient of C is 1.