A: boiling point of water at higher altitude is lower than `100^@C`
R: Boiling point is a colligative property.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that "the boiling point of water at higher altitude is lower than 100°C."

- **Explanation**: The boiling point of a liquid is the temperature at which its vapor pressure equals the atmospheric pressure. At higher altitudes, the atmospheric pressure is lower than at sea level. Therefore, water will boil at a temperature lower than 100°C because it requires a lower temperature for its vapor pressure to equal the reduced atmospheric pressure.

**Conclusion**: The assertion is **True**.

### Step 2: Analyze the Reason
The reason states that "boiling point is a colligative property."

- **Explanation**: Colligative properties are properties that depend on the number of solute particles in a solution but not on the identity of the solute. Examples include boiling point elevation and freezing point depression. However, the boiling point itself is not a colligative property; rather, it is an intrinsic property of a pure substance. The boiling point can vary depending on the substance and is not solely determined by the number of particles in a solution.

**Conclusion**: The reason is **False**.

### Final Conclusion
- **Assertion**: True
- **Reason**: False

Thus, the correct answer is that the assertion is true, and the reason is false.

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