Identify the materials, which can be classified as paramagnetic and diamagnetic: Al, Bi, Cu, Na.

Explanation

To classify the materials Al (Aluminum), Bi (Bismuth), Cu (Copper), and Na (Sodium) as paramagnetic or diamagnetic, we can follow these steps:

### Step 1: Understand the Definitions
- **Paramagnetic Materials**: These materials have unpaired electrons and are attracted to an external magnetic field. They do not retain magnetism once the external field is removed.
- **Diamagnetic Materials**: These materials have all their electrons paired and are weakly repelled by a magnetic field. They do not retain magnetism when the external field is removed.

### Step 2: Analyze Each Material
1. **Aluminum (Al)**:
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