An exothermic reaction is one which

Options

A. takes place only on heating
B. is accompanied with flame
C. is accompanied by evolution of heat
D. Is accompanied by absorption of heat.

Answer

**Step-by-Step Solution:**

1. **Understanding Exothermic Reactions**:
- An exothermic reaction is defined as a chemical reaction that releases energy to its surroundings. The term "exothermic" can be broken down into "exo," meaning outside, and "thermic," relating to heat.

2. **Energy Release**:
- In exothermic reactions, energy is typically released in the form of heat. This means that the temperature of the surroundings increases as the reaction proceeds.

3. **Evaluating Options**:
- **Option 1**: "Take place only on heating" - This is incorrect. Exothermic reactions can occur spontaneously without external heating.
- **Option 2**: "Is accompanied with flame" - This is also incorrect. While some exothermic reactions may produce flames, not all do.
- **Option 3**: "Is accompanied by evolution of heat" - This is correct. Exothermic reactions are characterized by the release of heat.
- **Option 4**: "Is accompanied by absorption of heat" - This is incorrect. Exothermic reactions do not absorb heat; they release it.

4. **Conclusion**:
- The correct definition of an exothermic reaction is that it is accompanied by the evolution of heat. Thus, the correct answer is the third option.

**Final Answer**: An exothermic reaction is one which is accompanied by the evolution of heat.

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