Burning of wood and coal causes _______ __of air.

Explanation

**Step-by-Step Solution:**

1. **Identify the materials being burned:** The question refers to the burning of wood and coal. Both of these materials are commonly used as fuels.

2. **Understand the combustion process:** When wood and coal are burned, they undergo a chemical reaction known as combustion. This process typically involves the reaction of carbon-based materials with oxygen in the air.

3. **Determine the products of combustion:** The combustion of wood and coal primarily produces several gases:
- Carbon monoxide (CO)
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