Define the conductivity of a conductor. Write its SI unit

Explanation

### Step-by-Step Solution:

1. **Definition of Conductivity**:
- Conductivity of a conductor is defined as the tendency of the conductor to allow the flow of electric charge. In most cases, this charge is carried by electrons in the material.

2. **Mathematical Representation**:
- Conductivity (σ) is the inverse of resistivity (ρ). It can be expressed mathematically as:
\[
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