Define relative density of a substance.

Explanation

To define the relative density of a substance, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Density**:
- Density is defined as the mass of a substance divided by its volume. The formula for density (ρ) is:
\[
\text{Density} (\rho) = \frac{\text{Mass (m)}}{\text{Volume (V)}}
...