Which of the following has the maximum vapour pressure?

Options

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

Answer

To determine which of the given compounds has the maximum vapor pressure, we can follow these steps:

### Step 1: Understand the Relationship Between Vapor Pressure and Boiling Point
Vapor pressure is inversely related to boiling point. This means that a substance with a lower boiling point will have a higher vapor pressure at a given temperature.

### Step 2: Identify the Compounds and Their Boiling Points
The compounds given are:
1. HCl (Hydrochloric acid)
2. HBr (Hydrobromic acid)
3. HF (Hydrofluoric acid)
4. HI (Hydroiodic acid)

We need to know the boiling points of these compounds:
- HCl: -85 °C
- HBr: -66.8 °C
- HF: 19.5 °C (due to strong hydrogen bonding)
- HI: -35 °C

### Step 3: Arrange the Compounds by Boiling Point
Now we can arrange these compounds in order of increasing boiling point:
1. HCl: -85 °C
2. HBr: -66.8 °C
3. HI: -35 °C
4. HF: 19.5 °C

### Step 4: Determine the Order of Vapor Pressure
Since vapor pressure is inversely proportional to boiling point, we can reverse the order of boiling points to find the order of vapor pressure:
1. HCl (highest vapor pressure)
2. HBr
3. HI
4. HF (lowest vapor pressure)

### Step 5: Conclusion
From our analysis, HCl has the highest vapor pressure among the given compounds.

### Final Answer
The compound with the maximum vapor pressure is **HCl**.

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