The S.I. unit of density is ........

Explanation

To find the S.I. unit of density, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Density**:
Density is defined as the mass of a substance per unit volume. This can be expressed mathematically as:
\[
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
...