The following species cannot exist in an aqueous solution?

Options

A. `NH_(4)^(+)`
B. `NH_(3)^(-)`
C. `NH_(3)`
D. `NH_(2)^(-)`

Answer

To determine which species cannot exist in an aqueous solution, we will analyze the given options one by one.

### Step-by-Step Solution:

1. **Understanding Aqueous Solutions**:
- An aqueous solution is one where water (H₂O) is the solvent. We need to consider how different species behave when dissolved in water.

2. **Analyzing NH₃ (Ammonia)**:
- When NH₃ is dissolved in water, it reacts with water to form NH₄⁺ (ammonium ion) and OH⁻ (hydroxide ion):
\[ \text{NH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4^+ + \text{OH}^- \]
- Since NH₃ can exist in aqueous solution as NH₄⁺ and OH⁻, it is not the answer.

3. **Analyzing NH₃⁻ (Amide Ion)**:
- The structure of NH₃⁻ includes three hydrogen atoms and two lone pairs, resulting in a negative charge.
- The hybridization would be S, P₃, D₁, which is not possible since nitrogen does not have d-orbitals.
- Therefore, NH₃⁻ cannot exist in aqueous solution.

4. **Analyzing NH₃ (again)**:
- As previously discussed, NH₃ can exist in water, forming NH₄⁺ and OH⁻. Thus, it is not the answer.

5. **Analyzing NH₂⁻ (Amide Ion)**:
- NH₂⁻ is a stronger base than OH⁻ due to the negative charge being more stable on oxygen than on nitrogen.
- When NH₂⁻ is placed in water, it will react to form NH₃ and OH⁻:
\[ \text{NH}_2^- + \text{H}_2\text{O} \rightarrow \text{NH}_3 + \text{OH}^- \]
- Since NH₂⁻ will react completely to form NH₃ and OH⁻, it cannot exist in aqueous solution.

6. **Conclusion**:
- The species that cannot exist in an aqueous solution are NH₃⁻ and NH₂⁻.

### Final Answer:
- The species that cannot exist in an aqueous solution are **NH₃⁻ and NH₂⁻**.