Which of the following is /are true when HCI (g) is passed through water?
(i) It does not ionise in the solution as it is a covalent compound .
(ii) It ionises in the solution.
(iii) It gives both hydrogen and hydroxyl ion in the solution
(iv) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule.

Options

A. Only (i)
B. Only (iii)
C. (ii) and (iv)
D. (iii) and (iv)

Explanation

To solve the question regarding the behavior of HCl (g) when passed through water, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding HCl in Water**:
When hydrogen chloride gas (HCl) is dissolved in water, it forms hydrochloric acid (HCl(aq)). This process involves the interaction of HCl with water molecules.

**Hint**: Remember that HCl is a polar covalent compound, which affects its behavior in water.

2. **Analyzing Statement (i)**:
The first statement claims that HCl does not ionize in the solution because it is a covalent compound. This is **false**. Although HCl is a covalent compound, it ionizes in water to form ions.

**Hint**: Consider the nature of polar covalent bonds and their ability to dissociate in polar solvents like water.

3. **Analyzing Statement (ii)**:
The second statement asserts that HCl ionizes in the solution. This is **true**. When HCl is dissolved in water, it dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻).

**Hint**: Think about how strong acids behave in water and what ions they produce.

4. **Analyzing Statement (iii)**:
The third statement suggests that HCl gives both hydrogen and hydroxyl ions in the solution. This is **false**. HCl produces hydrogen ions (H⁺) and chloride ions (Cl⁻), not hydroxyl ions (OH⁻).

**Hint**: Recall the ions produced by strong acids and the difference between hydroxyl and chloride ions.

5. **Analyzing Statement (iv)**:
The fourth statement states that HCl forms hydronium ions (H₃O⁺) in the solution due to the combination of hydrogen ions with water molecules. This is **true**. The H⁺ ions produced from HCl react with water to form hydronium ions.

**Hint**: Consider the process of protonation in aqueous solutions and how H⁺ interacts with water.

### Conclusion:
Based on the analysis:
- Statement (i) is **false**.
- Statement (ii) is **true**.
- Statement (iii) is **false**.
- Statement (iv) is **true**.

Thus, the true statements when HCl (g) is passed through water are (ii) and (iv).

### Final Answer:
The correct statements are (ii) and (iv), which corresponds to option number 3.