Which of the following is not a redox reaction?

Options

A. `H_(2)+Cl_(2) rarr 2 HCl`
B. `NaOH+HCl rarr NaCl+H_(2)O`
C. Photosynthesis
D. Cell respiration

Answer

To determine which of the given reactions is not a redox reaction, we need to analyze each option based on the definitions of oxidation and reduction. A redox reaction involves both oxidation (loss of electrons) and reduction (gain of electrons).

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions to analyze. Let's denote them as:
- Reaction 1: H2Cl2 → 2 HCl
- Reaction 2: NaOH + HCl → NaCl + H2O
- Reaction 3: Photosynthesis (6 CO2 + 6 H2O → C6H12O6 + 6 O2)
- Reaction 4: Cellular Respiration (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O)

2. **Analyze Reaction 1 (H2Cl2 → 2 HCl)**:
- Oxidation states:
- H2Cl2: H = 0, Cl = 0
- HCl: H = +1, Cl = -1
- Changes:
- H: 0 → +1 (oxidation, loss of electrons)
- Cl: 0 → -1 (reduction, gain of electrons)
- Conclusion: Both oxidation and reduction occur. This is a redox reaction.

3. **Analyze Reaction 2 (NaOH + HCl → NaCl + H2O)**:
- Oxidation states:
- NaOH: Na = +1, O = -2, H = +1
- HCl: H = +1, Cl = -1
- NaCl: Na = +1, Cl = -1
- H2O: H = +1, O = -2
- Changes:
- Na: +1 (no change)
- O: -2 (no change)
- H: +1 (no change)
- Cl: -1 (no change)
- Conclusion: No changes in oxidation states. This is **not** a redox reaction.

4. **Analyze Reaction 3 (Photosynthesis)**:
- Oxidation states:
- CO2: C = +4, O = -2
- H2O: H = +1, O = -2
- C6H12O6: C = 0 (calculated), O = -2
- Changes:
- C: +4 → 0 (reduction)
- O: -2 → 0 (oxidation)
- Conclusion: Both oxidation and reduction occur. This is a redox reaction.

5. **Analyze Reaction 4 (Cellular Respiration)**:
- Oxidation states:
- C6H12O6: C = 0, O = 0
- O2: O = 0
- CO2: C = +4, O = -2
- H2O: H = +1, O = -2
- Changes:
- C: 0 → +4 (oxidation)
- O: 0 → -2 (reduction)
- Conclusion: Both oxidation and reduction occur. This is a redox reaction.

6. **Final Conclusion**:
- The only reaction that does not involve a change in oxidation states is **Reaction 2 (NaOH + HCl → NaCl + H2O)**. Therefore, this is the reaction that is **not** a redox reaction.

### Answer:
The reaction that is not a redox reaction is **2. NaOH + HCl → NaCl + H2O**.