Which of the following halogen acid is a liquid ?

Options

A. HF
B. HCI
C. HBr
D. HI

Explanation

To determine which halogen acid is a liquid among the given options (HF, HCl, HBr, and HI), we can analyze the properties of each compound.

### Step-by-Step Solution:

1. **Understanding Halogen Acids**: Halogen acids are binary acids formed by hydrogen and halogens. The common halogen acids include HF (hydrofluoric acid), HCl (hydrochloric acid), HBr (hydrobromic acid), and HI (hydroiodic acid).

2. **State of Each Halogen Acid**:
- **HF (Hydrofluoric Acid)**: HF is known to form strong hydrogen bonds due to the high electronegativity of fluorine. These hydrogen bonds lead to a relatively high boiling point, allowing HF to exist as a liquid at room temperature.
- **HCl (Hydrochloric Acid)**: HCl is a gas at room temperature. It does not exhibit significant hydrogen bonding compared to HF, resulting in a lower boiling point.
- **HBr (Hydrobromic Acid)**: Similar to HCl, HBr is also a gas at room temperature and does not have strong hydrogen bonding.
- **HI (Hydroiodic Acid)**: HI is also a gas at room temperature and does not exhibit strong hydrogen bonding.

3. **Conclusion**: Among the options provided, only HF exists as a liquid at room temperature due to its ability to form hydrogen bonds, which increases its boiling point.

### Final Answer:
The halogen acid that is a liquid is **HF (Hydrofluoric Acid)**.

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