____ is the surest test of magnetisation.

Options

A. Rotation
B. Repulsion
C. Attraction
D. All of these

Explanation

**Step-by-Step Solution:**

1. **Understanding Magnetism**: To determine the surest test of magnetization, we need to understand how magnets interact with each other. There are two main types of interactions: attraction and repulsion.

2. **Attraction**: When a magnet is brought close to a magnetic material, it can attract the material regardless of whether the magnet's north or south pole is used. This means that attraction can occur in both scenarios, making it less reliable for testing magnetization.

3. **Repulsion**: In contrast, repulsion occurs only when like poles of magnets are brought close to each other. For example, if you bring the north pole of one magnet close to the north pole of another magnet, they will repel each other. This reaction is a clear indication that both objects are indeed magnets.

4. **Conclusion**: Since repulsion only occurs with like poles, it is the surest test of magnetization. If repulsion is observed, we can confidently conclude that the object being tested is a magnet. Therefore, the answer to the question is that **repulsion** is the surest test of magnetization.

**Final Answer**: Repulsion

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