Which equation represents the conservation of matter?

The equation that represents the conservation of matter must have the same number of atoms of each element on both sides of the equation.

Let's analyze the options:

1. **3H2O + 3CO2 → C6H12O6 + 6O2**
- Reactants: 3 H2O (6 H, 3 O) + 3 CO2 (3 C, 6 O) → total: 6 C, 12 H, 9 O
- Products: C6H12O6 (6 C, 12 H, 6 O) + 6 O2 (0 C, 0 H, 12 O) → total: 6 C, 12 H, 18 O
- Not balanced (O is not conserved).

2. **6H2O + 10CO2 → C6H12O6 + 4O2**
- Reactants: 6 H2O (12 H, 6 O) + 10 CO2 (10 C, 20 O) → total: 10 C, 12 H, 26 O
- Products: C6H12O6 (6 C, 12 H, 6 O) + 4 O2 (0 C, 0 H, 8 O) → total: 6 C, 12 H, 14 O
- Not balanced (C and O are not conserved).

3. **6H2O + 6CO2 → C6H12O6 + 6O2**
- Reactants: 6 H2O (12 H, 6 O) + 6 CO2 (6 C, 12 O) → total: 6 C, 12 H, 18 O
- Products: C6H12O6 (6 C, 12 H, 6 O) + 6 O2 (0 C, 0 H, 12 O) → total: 6 C, 12 H, 18 O
- Balanced! This equation conserves matter.

4. **6H2O + 6CO2 → C3H6O3 + 3O2**
- Reactants: 6 H2O (12 H, 6 O) + 6 CO2 (6 C, 12 O) → total: 6 C, 12 H, 18 O
- Products: C3H6O3 (3 C, 6 H, 3 O) + 3 O2 (0 C, 0 H, 6 O) → total: 3 C, 6 H, 9 O
- Not balanced (C, H, and O are not conserved).

Thus, the only equation that accurately represents the conservation of matter is:

**3. 6H2O + 6CO2 → C6H12O6 + 6O2**