Give two examples for each of the following cases :
(a) physical changes which are reversible .

Explanation

### Step-by-Step Solution

1. **Understanding Physical Changes**:
- Physical changes are processes where the form of a substance changes, but its chemical composition remains the same. No new substances are formed during these changes.

2. **Identifying Reversible Physical Changes**:
- A reversible physical change is one where the original substance can be recovered after the change has occurred.

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