Select equation having endothermic step:

Options

A. `S^(-)(g) to S^(2-)(g)`
B. `Na^(+)(g) +Cl^(-)(g) to NaCl(s)`
C. `N(g) to N^(-)(g)`
D. `Al^(2+)(g) to Al^(3+)(g)`

Answer

To determine which equations represent endothermic processes, we need to understand the concept of endothermic reactions. An endothermic reaction is characterized by a positive change in enthalpy (ΔH > 0), meaning that the reaction absorbs energy from its surroundings.

### Step-by-Step Solution:

1. **Understanding Endothermic Processes**:
- An endothermic process is one that absorbs energy. This is indicated by a positive change in enthalpy (ΔH > 0).

2. **Analyzing Given Equations**:
- We need to analyze the provided equations to see which ones involve the absorption of energy.

3. **Identifying the First Equation**:
- The first equation involves sulfur (S) accepting an electron to form a stable divalent anion (S²⁻). This process requires energy to overcome the electrostatic repulsion between the monovalent anion and the incoming electron. Therefore, this step is endothermic.

4. **Identifying the Second Equation**:
- The second equation involves nitrogen (N) gaining an electron to form N⁻. Nitrogen has a strong electron affinity due to its stable half-filled p-orbital configuration. The process of gaining an electron requires energy, making this step endothermic as well.

5. **Identifying the Third Equation**:
- The third equation involves the removal of an electron from Al²⁺ to form Al³⁺. This process requires energy to remove an electron from a positively charged ion, indicating that this step is also endothermic.

6. **Conclusion**:
- Based on the analysis, the equations that represent endothermic processes are:
- The formation of S²⁻ from S⁻.
- The formation of N⁻ from N.
- The formation of Al³⁺ from Al²⁺.

### Final Answer:
The equations having endothermic steps are those involving the formation of S²⁻, N⁻, and Al³⁺.

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