All combustion reactions are ...........

Explanation

**Step-by-Step Solution:**

1. **Understanding Combustion Reactions**:
Combustion reactions are chemical reactions that typically involve a substance (usually a hydrocarbon) reacting with oxygen (O₂) to produce heat and light.

2. **Identifying the Nature of Combustion Reactions**:
In these reactions, energy is released in the form of heat. This is a key characteristic of combustion reactions.

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