In which of the following reactions does `NH_(3)` act as a acid?

Options

A. `NH_(3)+H^(+)rarrNH_(4)`
B. `NH_(3)+H^(+)rarrNH_(2)^(-)+H_(2)`
C. `NH_(3)+HClrarrNH_(4)Cl`
D. None as `NH_(3)` is a base

Explanation

To determine in which of the given reactions ammonia (NH₃) acts as an acid, we need to understand the definition of an acid and a base according to the Brønsted-Lowry theory. An acid is a substance that donates a proton (H⁺ ion), while a base is a substance that accepts a proton.

Let's analyze each reaction step by step:

### Step 1: Analyze the First Reaction
**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 in this reaction.

**Hint:** Look for whether NH₃ is donating or accepting protons to determine its role.

### Step 2: Analyze the Second Reaction
**Reaction:** NH₃ + H⁺ → NH₂⁻ + H₂

- Here, NH₃ is releasing a proton (H⁺) and forming NH₂⁻.
- Since NH₃ is donating a proton, it is acting as an acid in this reaction.

**Hint:** Identify if NH₃ is releasing H⁺ ions to see if it acts as an acid.

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

- In this case, NH₃ is accepting a proton from HCl to form NH₄⁺.
- Therefore, NH₃ is acting as a base in this reaction.

**Hint:** Check if NH₃ is forming a positive ion (NH₄⁺) to confirm its role as a base.

### Step 4: Analyze the Fourth Reaction
**Reaction:** (Assuming a generic reaction where NH₃ is stated to be a base)

- If it is clearly stated that NH₃ is acting as a base, we can conclude that it is not acting as an acid in this reaction.

**Hint:** If the reaction states that NH₃ is a base, it is not acting as an acid.

### Conclusion
From the analysis of the reactions, we find that NH₃ acts as an acid only in the second reaction.

**Final Answer:** NH₃ acts as an acid in the second reaction.