Ammonia is a weak base that reacts with water according to the equation
`NH_(3)(aq)+H_(2)O(l)hArrNH_(4)^(+)(aq)+OH^(-)(aq)`
Select the correct option (s) that can increase the moles of ammonium ion in water:

Options

A. Addition of HCl
B. Addition of NaOH
C. Additon of `NH_(4)Cl`
D. Addition of `H_(2)O`

Answer

To solve the question regarding which options can increase the moles of ammonium ion in water, we need to analyze the provided reactions and the effects of each option on the equilibrium of the reaction.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The reaction given is:
\[ NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq) \]
This shows that ammonia (NH₃) reacts with water to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻).

2. **Analyzing Each Option**:
- **Option A: Addition of HCl**:
- HCl is a strong acid that will dissociate completely to give H⁺ ions. The addition of H⁺ ions will react with OH⁻ ions to form water, reducing the concentration of OH⁻. However, this does not directly increase the moles of NH₄⁺ because the equilibrium will not shift significantly to produce more NH₄⁺. Thus, this option is **incorrect**.

- **Option B: Addition of NaOH**:
- NaOH is a strong base that dissociates to give Na⁺ and OH⁻ ions. The increase in OH⁻ concentration will shift the equilibrium to the left (backward direction) to reduce the concentration of OH⁻. This means that the moles of NH₄⁺ will decrease. Therefore, this option is **incorrect**.

- **Option C: Addition of Ammonium Chloride (NH₄Cl)**:
- Ammonium chloride will dissociate into NH₄⁺ and Cl⁻ ions. The addition of NH₄⁺ will increase its concentration. However, according to Le Chatelier's principle, the equilibrium will shift to the left to counteract the increase in NH₄⁺ concentration, thus not significantly increasing the moles of NH₄⁺. Hence, this option is also **incorrect**.

- **Option D: Addition of Water**:
- Adding water increases the concentration of the reactants (NH₃ and H₂O). According to Le Chatelier's principle, the equilibrium will shift to the right (forward direction) to produce more products (NH₄⁺ and OH⁻). Therefore, the moles of NH₄⁺ will increase. This option is **correct**.

3. **Conclusion**:
The only option that increases the moles of ammonium ion in water is the addition of water.

### Final Answer:
The correct option is **D: Addition of Water**.