What is radioactivity ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Radioactivity**: Radioactivity is defined as the phenomenon of spontaneous disintegration of the nucleus of an unstable atom.

2. **Process of Radioactivity**: During this process, the unstable nucleus loses energy by emitting particles or radiation. This emission occurs as the nucleus seeks a more stable configuration.

3. **Types of Radiation Emitted**: The radiation emitted during radioactivity can take various forms, including:
- **Alpha Radiation**: Consists of alpha particles (helium nuclei).
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