An antibiotic is

Options

A. Chloramphenicol
B. Ethephon
C. Phosphon-D
D. AMO-1618.

Answer

**Step-by-Step Solution:**

1. **Understanding Antibiotics**:
- Antibiotics are substances produced by microorganisms (like bacteria and fungi) that can kill or inhibit the growth of other bacteria. The term "antibiotic" literally means "against life," but in this context, it specifically refers to their action against bacterial infections.

2. **Analyzing the Options**:
- The question provides four options: chloramphenicol, ethiphone, phosphon D, and AMO 1618. We need to identify which of these is an antibiotic.

3. **Evaluating Each Option**:
- **Chloramphenicol**: This is a well-known antibiotic that is widely used to treat various bacterial infections. It works by inhibiting protein synthesis in bacteria by binding to the 50S ribosomal subunit. This prevents the formation of polysomes, which are necessary for protein synthesis.
- **Ethyphone**: This is not an antibiotic; it is a synthetic plant growth regulator that promotes fruit ripening and causes abscission in plants.
- **Phosphon D and AMO 1618**: Both of these are plant growth inhibitors. They inhibit the action of gibberellins, which are plant hormones. Therefore, they are not antibiotics.

4. **Conclusion**:
- Based on the analysis, the only option that qualifies as an antibiotic is **chloramphenicol**.

**Final Answer**: An antibiotic is **chloramphenicol**.

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