Incomplete combustion of coal and petroleum:
(i) increases air pollution.
(ii) increases efficiency of machines.
(iii) reduces global warming.
(iv) produce poisonous gases.

Options

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

Explanation

To solve the question regarding the effects of incomplete combustion of coal and petroleum, we will analyze each statement provided:

1. **Statement (i): Increases air pollution.**
- Incomplete combustion of coal and petroleum leads to the release of pollutants, including carbon monoxide (CO), which is a harmful gas. Therefore, this statement is **true**.

2. **Statement (ii): Increases efficiency of machines.**
- Incomplete combustion does not increase the efficiency of machines. In fact, it often leads to lower efficiency because not all fuel is converted into usable energy. Hence, this statement is **false**.

3. **Statement (iii): Reduces global warming.**
- Incomplete combustion typically produces more carbon dioxide (CO2) and other greenhouse gases, which contribute to global warming rather than reducing it. Therefore, this statement is **false**.

4. **Statement (iv): Produces poisonous gases.**
- As mentioned earlier, incomplete combustion produces carbon monoxide, which is indeed a poisonous gas. Thus, this statement is **true**.

Based on this analysis, the correct statements are (i) and (iv). Therefore, the answer to the question is that incomplete combustion of coal and petroleum increases air pollution and produces poisonous gases.

### Final Answer:
The correct statements are (i) increases air pollution and (iv) produces poisonous gases.