Which one of the following demonstrates a decrease in entropy ?

Options

A. Dissolving a solid into solution
B. An expanding universe
C. Burning a log in a fire place
D. Raking up leaves into a trash bag

Explanation

To determine which process demonstrates a decrease in entropy, let's analyze the options provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Entropy**:
Entropy is a measure of disorder or randomness in a system. A higher entropy indicates more disorder, while a lower entropy indicates more order.

2. **Analyzing the First Process - Dissolving a Solid**:
- When a solid (like NaCl) dissolves in water, it breaks into ions (Na⁺ and Cl⁻).
- This process increases the disorder because the solid structure is broken down into individual ions that are free to move in the solution.
- **Conclusion**: This process increases entropy.

3. **Analyzing the Second Process - Expanding Universe**:
- The expansion of the universe, as described in the Big Bang theory, leads to the formation of various celestial bodies and a distribution of matter.
- This process also increases disorder as the universe expands and matter spreads out.
- **Conclusion**: This process increases entropy.

4. **Analyzing the Third Process - Burning a Log**:
- When wood (log) burns, it converts into gases (like CO₂) and ash.
- The solid wood is transformed into gaseous products, which are more disordered than the solid form.
- **Conclusion**: This process increases entropy.

5. **Analyzing the Fourth Process - Raking Leaves into a Trash Bag**:
- When leaves are raked together into a trash bag, they go from a scattered arrangement to a more organized state within the bag.
- This process reduces disorder as the leaves are collected and organized in one place.
- **Conclusion**: This process decreases entropy.

### Final Answer:
The process that demonstrates a decrease in entropy is **Raking up leaves into a trash bag**.