In which of the following reaction does `NH_(3)` acts as an acid?

Options

A. `NH_(3) +H^(+) toNH_(4)^(+)`
B. `NH_(3)+Nato NaNH_(2)+(1)/(2)H_(2)`
C. `NH_(3) +HCl toNH_(4) CI`
D. None of the above

Answer

To determine in which reaction ammonia (NH₃) acts as an acid, we need to understand the definition of an acid in the context of Brønsted-Lowry theory, which states that an acid is a substance that donates protons (H⁺ ions).

Let's analyze the given options step by step:

### Step 1: Analyze Option 1
**Reaction:** NH₃ + H⁺ → NH₄⁺

- In this reaction, NH₃ is accepting a proton (H⁺) to form NH₄⁺.
- Since NH₃ is accepting a proton, it is acting as a base, not an acid.

**Conclusion:** Option 1 is incorrect.

### Step 2: Analyze Option 2
**Reaction:** NH₃ + Na → NaNH₂ + ½ H₂

- In this reaction, NH₃ is reacting with sodium (Na) to produce NaNH₂ and hydrogen gas (H₂).
- Here, NH₃ donates a proton to sodium, which results in the formation of NaNH₂.
- Since NH₃ is donating a proton in this reaction, it is acting as an acid.

**Conclusion:** Option 2 is correct.

### Step 3: Analyze Option 3
**Reaction:** NH₃ + HCl → NH₄Cl

- In this reaction, NH₃ is reacting with hydrochloric acid (HCl) to form ammonium chloride (NH₄Cl).
- HCl is a strong acid that donates a proton (H⁺), and NH₃ accepts this proton to form NH₄⁺.
- Therefore, in this case, NH₃ is acting as a base because it is accepting a proton.

**Conclusion:** Option 3 is incorrect.

### Step 4: Analyze Option 4
**Reaction:** None of the above

- Since we have already determined that Option 2 is correct, Option 4 (none of the above) cannot be the answer.

**Conclusion:** Option 4 is incorrect.

### Final Answer
The correct answer is **Option 2**, where NH₃ acts as an acid by donating a proton.

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