Which of the following does not form during glycolysis?

Options

A. NADH
B. ATP
C. Pyruvate
D. `FADH_2`

Explanation

**Step-by-Step Solution:**

1. **Understand Glycolysis**: Glycolysis is the metabolic process that breaks down glucose into two molecules of pyruvate. It is the first step in cellular respiration.

2. **Identify Products of Glycolysis**: During glycolysis, several key products are formed:
- Two molecules of pyruvate
- ATP (adenosine triphosphate)
- NADH (nicotinamide adenine dinucleotide)

3. **Analyze the Options**: The question asks which of the following does not form during glycolysis. The options typically include:
- NADH
- ATP
- Pyruvate
- FADH2

4. **Determine the Incorrect Option**:
- NADH, ATP, and pyruvate are all products of glycolysis.
- FADH2 is not produced during glycolysis; it is formed during the Krebs cycle (also known as the citric acid cycle).

5. **Conclude the Answer**: Therefore, the correct answer to the question "Which of the following does not form during glycolysis?" is **FADH2**.

**Final Answer**: FADH2 (Option D)

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