What is SI unit of activity of Radioactive substance ?

Explanation

To determine the SI unit of the activity of a radioactive substance, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Radioactivity**:
- Radioactivity refers to the process by which unstable atomic nuclei lose energy by emitting radiation. This emission can occur in the form of alpha particles, beta particles, or gamma rays.

2. **Defining Activity**:
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