Which of the following statements are true?
(i) Cigarette smoke is a source of carbon monoxide.
(ii) Smog is a combination of smoke and fog which mainly contains CFCs.
(iii) Burning of coal releases fly ash.
(iv) Acid rain increases the pH of rivers and lakes.

Options

A. (i) and (ii)
B. (i) and (iii)
C. (ii) and (iv)
D. (iii) and (iv)

Answer

To determine which statements are true, let's analyze each statement one by one:

1. **Statement (i)**: "Cigarette smoke is a source of carbon monoxide."
- **Analysis**: This statement is true. Cigarette smoke contains a significant amount of carbon monoxide, which can bind with hemoglobin in the blood, reducing the oxygen-carrying capacity.

2. **Statement (ii)**: "Smog is a combination of smoke and fog which mainly contains CFCs."
- **Analysis**: This statement is false. While smog is indeed a combination of smoke and fog, it primarily contains pollutants like sulfur dioxide (SO2) and particulate matter, not chlorofluorocarbons (CFCs), which are mainly found in refrigeration and air conditioning.

3. **Statement (iii)**: "Burning of coal releases fly ash."
- **Analysis**: This statement is true. When coal is burned, it produces fly ash, which is a byproduct consisting of fine particles that are carried away with the flue gases.

4. **Statement (iv)**: "Acid rain increases the pH of rivers and lakes."
- **Analysis**: This statement is false. Acid rain actually decreases the pH of water bodies, making them more acidic, which can harm aquatic life.

**Conclusion**: The true statements are (i) and (iii).

### Summary of True Statements:
- (i) Cigarette smoke is a source of carbon monoxide. **(True)**
- (ii) Smog is a combination of smoke and fog which mainly contains CFCs. **(False)**
- (iii) Burning of coal releases fly ash. **(True)**
- (iv) Acid rain increases the pH of rivers and lakes. **(False)**

### Final Answer:
The correct statements are (i) and (iii).

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