How many of the following reactions proceed with the absorption of energy?
`Cl(g) to CI^(-)(g)`
`O^(2-) (g) to O^(-)(g)`
`N(g) to N^(-)(g)`
`Mg(g) to Mg^(2+)(g)`
`Cl^(-)(g) to Cl^(2-)(g)`
`Be(g) to Be^(-)(g)`

Answer

To determine how many of the given reactions proceed with the absorption of energy, we need to analyze each reaction in terms of whether energy is absorbed (endothermic) or released (exothermic).

### Step-by-Step Solution:

1. **Reaction: Cl(g) to Cl^(-)(g)**
- In this reaction, a chlorine atom gains an electron to become a chloride ion.
- This process releases energy because adding an electron to a neutral atom generally releases energy (exothermic).
- **Conclusion**: This reaction does not absorb energy.

2. **Reaction: O^(2-)(g) to O^(-)(g)**
- Here, an oxide ion (O^(2-)) loses an electron to become a superoxide ion (O^(-)).
- Removing an electron requires energy input (endothermic).
- **Conclusion**: This reaction absorbs energy.

3. **Reaction: N(g) to N^(-)(g)**
- In this case, a nitrogen atom gains an electron to become a nitride ion (N^(-)).
- Similar to the first reaction, adding an electron to a neutral atom releases energy (exothermic).
- **Conclusion**: This reaction does not absorb energy.

4. **Reaction: Mg(g) to Mg^(2+)(g)**
- Here, magnesium loses two electrons to become a magnesium ion (Mg^(2+)).
- Removing electrons requires energy input (endothermic).
- **Conclusion**: This reaction absorbs energy.

5. **Reaction: Cl^(-)(g) to Cl^(2-)(g)**
- In this reaction, a chloride ion gains an electron to become a dichloride ion (Cl^(2-)).
- Adding an electron to a negatively charged ion involves overcoming electron-electron repulsion, which requires energy (endothermic).
- **Conclusion**: This reaction absorbs energy.

6. **Reaction: Be(g) to Be^(-)(g)**
- Here, a beryllium atom gains an electron to become a beryllide ion (Be^(-)).
- Adding an electron to a neutral atom generally releases energy (exothermic).
- **Conclusion**: This reaction does not absorb energy.

### Summary of Results:
- Reactions that absorb energy: O^(2-) to O^(-), Mg to Mg^(2+), Cl^(-) to Cl^(2-).
- Total reactions that absorb energy: **3**

### Final Answer:
**3 reactions proceed with the absorption of energy.**

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