Which of the following reactions is not correct according to the law of conservation of mass?

Options

A. `2Mg(s)+O_(2)(g)rarr2MgO(s)`
B. `C_(3)H_(3)(g)+O_(2)(g)rarrCO_(2)(g)+H_(2)O(g)`
C. `P_(4)(s)+5O_(2)(g)rarrP_(4)O_(10)(s)`
D. `CH_(4)(g)+2O_(2)(g)rarrCO_(2)(g)+2H_(2)O(g)`

Explanation

To determine which reaction does not adhere to the law of conservation of mass, we need to analyze each reaction provided and ensure that the total mass of the reactants equals the total mass of the products.

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions to analyze:
- Reaction 1: \( 2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO} \)
- Reaction 2: \( \text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \)
- Reaction 3: \( \text{P}_4 + 5 \text{O}_2 \rightarrow \text{P}_4\text{O}_{10} \)
- Reaction 4: \( \text{CH}_4 + 2 \text{O}_2 \rightarrow \text{CO}_2 + 2 \text{H}_2\text{O} \)

2. **Calculate Mass of Reactants and Products for Each Reaction**:
- **Reaction 1**:
- Reactants: \( 2 \text{Mg} \) (2 × 24 = 48) + \( \text{O}_2 \) (2 × 16 = 32) = 48 + 32 = 80
- Products: \( 2 \text{MgO} \) (2 × 24 + 16 = 64) = 80
- **Conclusion**: Mass of reactants = Mass of products (80 = 80)

- **Reaction 2**:
- Reactants: \( \text{C}_3\text{H}_8 \) (3 × 12 + 8 × 1 = 36 + 8 = 44) + \( \text{O}_2 \) (2 × 16 = 32) = 44 + 32 = 76
- Products: \( \text{CO}_2 \) (12 + 32 = 44) + \( \text{H}_2\text{O} \) (2 × 1 + 16 = 2 + 16 = 18) = 44 + 18 = 62
- **Conclusion**: Mass of reactants ≠ Mass of products (76 ≠ 62)

- **Reaction 3**:
- Reactants: \( \text{P}_4 \) (4 × 31 = 124) + \( 5 \text{O}_2 \) (5 × 32 = 160) = 124 + 160 = 284
- Products: \( \text{P}_4\text{O}_{10} \) (124 + 160 = 284)
- **Conclusion**: Mass of reactants = Mass of products (284 = 284)

- **Reaction 4**:
- Reactants: \( \text{CH}_4 \) (12 + 4 = 16) + \( 2 \text{O}_2 \) (2 × 32 = 64) = 16 + 64 = 80
- Products: \( \text{CO}_2 \) (12 + 32 = 44) + \( 2 \text{H}_2\text{O} \) (2 × 18 = 36) = 44 + 36 = 80
- **Conclusion**: Mass of reactants = Mass of products (80 = 80)

3. **Identify the Incorrect Reaction**:
- From the analysis, **Reaction 2** \( \text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \) does not follow the law of conservation of mass because the mass of the reactants (76) does not equal the mass of the products (62).

### Final Answer:
The reaction that is not correct according to the law of conservation of mass is:
**\( \text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \)**