Ion which is not present in dilute HCl.

Options

A. `H^(+)`
B. `H_(3)O^(+)`
C. `Cl^(-)`
D. `HCl`

Answer

To determine which ion is not present in dilute HCl, we can analyze the dissociation of hydrochloric acid in water.

### Step-by-Step Solution:

1. **Understanding the Composition of Dilute HCl:**
- Dilute HCl is a solution of hydrochloric acid in water. The chemical formula for hydrochloric acid is HCl.

2. **Dissociation of HCl in Water:**
- When HCl is dissolved in water, it dissociates completely into its ions:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
- However, in the presence of water, the hydrogen ions (H⁺) do not exist freely. Instead, they associate with water molecules to form hydronium ions (H₃O⁺):
\[ \text{H}^+ + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ \]

3. **Identifying the Ions Present:**
- From the dissociation, we can conclude that in a dilute HCl solution, the following ions are present:
- Hydronium ion (H₃O⁺)
- Chloride ion (Cl⁻)

4. **Identifying the Ion Not Present:**
- Although H⁺ is produced during the dissociation, it is not present in the solution as a free ion. Instead, it exists as part of the hydronium ion (H₃O⁺). Therefore, the ion that is not present in dilute HCl is H⁺.

5. **Conclusion:**
- The ion which is not present in dilute HCl is H⁺.

### Final Answer:
- The ion which is not present in dilute HCl is **H⁺**.