Carbon monoxide is formed when coal or coke or charcoal is burnt in limited supply of oxygen.

Explanation

### Step-by-Step Text Solution:

1. **Understanding the Reaction**: When coal, coke, or charcoal is burned, the amount of oxygen available during the combustion process determines the products formed.

2. **Combustion in Sufficient Oxygen**:
- When there is a **sufficient supply of oxygen**, the combustion of carbon-based materials like coal, coke, or charcoal results in the formation of **carbon dioxide (CO₂)** and **water (H₂O)**.
- The reaction can be represented as:
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