In which of the following changes does entropy decrease ?

Options

A. Crystallisation of sucrose from solution
B. Dissolving sucrose in water
C. Melting of ice
D. Vapourisation of camphor.

Explanation

To determine in which of the following changes entropy decreases, we need to analyze each option based on the concept of entropy, which is a measure of the disorder or randomness of a system. Here’s a step-by-step breakdown:

1. **Understand Entropy**: Entropy is a measure of the randomness or disorder in a system. Generally, when a system becomes more ordered, entropy decreases, and when it becomes less ordered, entropy increases.

2. **Analyze Each Option**:
- **Option 1: Crystallization of sucrose from solution**:
- In this process, a liquid solution of sucrose turns into solid crystals.
- The movement of sucrose molecules becomes restricted as they form a solid structure, leading to a decrease in disorder.
- **Conclusion**: Entropy decreases.

- **Option 2: Dissolving sucrose in water**:
- Here, solid sucrose dissolves in water to form a solution.
- The solid sucrose molecules gain freedom of movement as they disperse in the liquid, increasing disorder.
- **Conclusion**: Entropy increases.

- **Option 3: Melting of ice**:
- Ice (solid) melts to form water (liquid).
- The structured arrangement of ice molecules breaks down, allowing for greater movement and disorder in the liquid state.
- **Conclusion**: Entropy increases.

- **Option 4: Vaporization of camphor**:
- Camphor transitions from solid to gas.
- The gaseous state has much greater molecular movement and disorder compared to the solid state.
- **Conclusion**: Entropy increases.

3. **Final Conclusion**:
- Among the options analyzed, the only process where entropy decreases is the **crystallization of sucrose from solution** (Option 1).

### Summary:
The correct answer is **Option 1: Crystallization of sucrose from solution**, as this process results in a decrease in entropy.