Assertion Two turns of krebs' cycle occurs per glucose molecules used.
reason Each turn of krebs' cycle produces 3NADH,`1FADH_2` and 1ATP molecules.

Explanation

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states that "Two turns of Krebs' cycle occur per glucose molecule used."

- **Explanation**: In cellular respiration, one glucose molecule (C6H12O6) is broken down through glycolysis to produce two molecules of pyruvate. Each pyruvate then enters the Krebs cycle (also known as the citric acid cycle). Since one glucose molecule produces two pyruvate molecules, it results in two turns of the Krebs cycle. Therefore, the assertion is true.

### Step 2: Analyze the Reason
The reason states that "Each turn of the Krebs cycle produces 3 NADH, 1 FADH2, and 1 ATP molecule."

- **Explanation**: During one complete turn of the Krebs cycle, the following products are generated:
- 3 NADH
- 1 FADH2
- 1 ATP (or GTP, depending on the cell type)

Since there are two turns of the Krebs cycle per glucose molecule, the total yield from one glucose molecule would be:
- 6 NADH (3 NADH per turn × 2 turns)
- 2 FADH2 (1 FADH2 per turn × 2 turns)
- 2 ATP (1 ATP per turn × 2 turns)

Thus, the reason is also true.

### Step 3: Determine the Relationship Between Assertion and Reason
Now we need to determine if the reason correctly explains the assertion.

- The assertion is true because two turns of the Krebs cycle occur for each glucose molecule.
- The reason is true and provides correct information about the products of the Krebs cycle, but it does not directly explain why two turns occur per glucose molecule. It simply states what is produced in each turn.

### Conclusion
Since both the assertion and reason are true, but the reason does not provide a correct explanation for the assertion, the correct answer is:

**Option 2: Both assertion and reason are true, but reason is not the correct explanation of the assertion.**

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