During chemical reaction only _________ electrons participate.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which type of electrons participate in a chemical reaction.

2. **Identifying Electron Types**: Electrons in an atom can be categorized into two types:
- **Valence Electrons**: These are the electrons in the outermost shell of an atom and are involved in chemical bonding and reactions.
- **Core Electrons**: These are the electrons in the inner shells and do not participate in chemical reactions.

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