A strong mutagen is

Options

A. Cold
B. Heat
C. Water
D. X-ray induced mutations

Answer

### Step-by-Step Solution:

1. **Understanding the Term "Mutagen":**
- A mutagen is a substance or factor that causes mutations in the DNA sequence. Mutations can lead to changes in the genetic material, which may affect an organism's traits.

2. **Identifying Mutations:**
- Mutations refer to any alteration in the DNA sequence. This can include point mutations (changes in a single base pair), insertions, deletions, or larger chromosomal changes.

3. **Analyzing the Options:**
- The question provides several options: cold, heat, water, and x-ray-induced mutations. We need to determine which of these is a strong mutagen.

4. **Evaluating Each Option:**
- **Cold:** Generally does not cause mutations; it is not a mutagen.
- **Heat:** While extreme heat can cause some damage, it is not typically classified as a strong mutagen.
- **Water:** Water is essential for life and does not cause mutations.
- **X-ray-induced mutations:** X-rays are a form of high-energy radiation known to cause damage to DNA, leading to mutations.

5. **Conclusion:**
- Among the given options, x-ray-induced mutations are the most appropriate choice as a strong mutagen. X-rays can cause significant damage to DNA, leading to various types of mutations, including point mutations.

### Final Answer:
- The correct answer is **x-ray-induced mutations** (Option 4).

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