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 following reactions is not a redox reaction, we need to analyze each option based on the changes in oxidation states of the elements involved. A redox reaction involves both oxidation (loss of electrons) and reduction (gain of electrons).

### Step-by-Step Solution:

1. **Identify the Reactions**:
We need to analyze the given reactions to see if they involve changes in oxidation states.

2. **Option 1: H2 + Cl2 → 2 HCl**
- Oxidation states:
- H2: H = 0 (elemental form)
- Cl2: Cl = 0 (elemental form)
- HCl: H = +1, Cl = -1
- Changes:
- H goes from 0 to +1 (oxidation)
- Cl goes from 0 to -1 (reduction)
- Conclusion: This is a redox reaction.

3. **Option 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 remains +1, Cl remains -1, H remains +1, O remains -2.
- Conclusion: There are no changes in oxidation states. This is **not a redox reaction**.

4. **Option 3: Photosynthesis (6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2)**
- Oxidation states:
- CO2: C = +4, O = -2
- H2O: H = +1, O = -2
- C6H12O6: C = 0 (average), O = -2
- O2: O = 0
- Changes:
- C goes from +4 to 0 (reduction)
- O goes from -2 to 0 (oxidation)
- Conclusion: This is a redox reaction.

5. **Option 4: Cellular Respiration (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O)**
- Oxidation states:
- C6H12O6: C = 0 (average), O = -2
- O2: O = 0
- CO2: C = +4, O = -2
- H2O: H = +1, O = -2
- Changes:
- C goes from 0 to +4 (oxidation)
- O goes from 0 to -2 (reduction)
- Conclusion: This is a redox reaction.

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