Various chemical substances inhibit respiration at various steps. Find out the incorrectly matched pair :-

Options

A. Cyanide – Prevents flow of electrons from cyt. `a_(3)` to `O_(2)`
B. 2, 4-DNP – Prevents synthesis of ATP from ADP and `Pi
C. Rotenone – Prevents transfer of electron from cyt b to cyt `C_(1)`
D. CO – Prevents flow of electrons from cyt `a_(3)` to `O_(2)`

Answer

To solve the question regarding the incorrectly matched pair of chemical substances that inhibit respiration, we will analyze each option provided:

### Step-by-Step Solution:

1. **Understanding the Inhibition of Respiration**:
- Respiration involves a series of biochemical reactions where electrons are transferred through various complexes in the electron transport chain, ultimately leading to ATP synthesis. Different inhibitors act at specific points in this process.

2. **Analyzing the Options**:
- **Option 1: Cyanide** - It is known to inhibit the flow of electrons from cytochrome A3 to oxygen. Cyanide acts on complex IV of the electron transport chain. This statement is correct.

- **Option 2: 2,4-DNP** - This compound is an uncoupler that prevents ATP synthesis from ADP and inorganic phosphate (Pi) by dissipating the proton gradient. This statement is also correct.

- **Option 3: Rotenone** - The statement claims that rotenone prevents the transfer of electrons from cytochrome B to cytochrome C1. However, rotenone actually inhibits complex I, preventing the transfer of electrons from complex I to ubiquinone, not from cytochrome B to cytochrome C1. Therefore, this statement is incorrect.

- **Option 4: Carbon Monoxide** - Similar to cyanide, carbon monoxide inhibits the flow of electrons from cytochrome A3 to oxygen, acting on complex IV. This statement is correct.

3. **Identifying the Incorrectly Matched Pair**:
- From the analysis, it is clear that **Option 3 (Rotenone)** is incorrectly matched because it does not inhibit the transfer of electrons from cytochrome B to cytochrome C1, but rather from complex I to ubiquinone.

### Conclusion:
The incorrectly matched pair is **Option 3: Rotenone prevents transfer of electrons from cytochrome B to cytochrome C1**.

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