Which of the following statements are not true for antibiotics ?
I. They are produced wholly or partly by chemical synthesis
II. In low concentrations, they inhibit the growth or destroy microorganisms by intervening in their metabolic processes
III. Even in low doses, they are highly toxic for humans
IV. They are products of microorganisms as purely synthetic compounds can never have antibacterial activity

Options

A. III, IV
B. I,II
C. II, IV
D. I, III

Answer

To determine which statements about antibiotics are not true, let's analyze each statement one by one.

### Step 1: Analyze Statement I
**Statement I:** They are produced wholly or partly by chemical synthesis.

- **Analysis:** This statement is true. Antibiotics can be produced through natural processes (from microorganisms) or can be synthesized chemically, either wholly or in part.

### Step 2: Analyze Statement II
**Statement II:** In low concentrations, they inhibit the growth or destroy microorganisms by intervening in their metabolic processes.

- **Analysis:** This statement is also true. Antibiotics are effective at low concentrations and can inhibit the growth or destroy bacteria by targeting their metabolic processes.

### Step 3: Analyze Statement III
**Statement III:** Even in low doses, they are highly toxic for humans.

- **Analysis:** This statement is not true. While high doses of antibiotics can be toxic, low doses are generally safe for humans and are often used therapeutically.

### Step 4: Analyze Statement IV
**Statement IV:** They are products of microorganisms as purely synthetic compounds can never have antibacterial activity.

- **Analysis:** This statement is also not true. There are purely synthetic antibiotics that have been developed and are effective against bacteria. Therefore, this statement is incorrect.

### Conclusion
Based on the analysis:
- **Statements III and IV are not true for antibiotics.**

### Final Answer
The statements that are not true for antibiotics are **III and IV**.

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