What is the SI unit of density?
(A) gcm−3

(B) gm−3

(C) Kgm−3

(D) Kgcm−3

To determine the SI unit of density, we first need to understand what density is. Density is defined as mass per unit volume. The formula for density (\( \rho \)) is:

\[
\rho = \frac{m}{V}
\]

where:
- \( m \) is the mass, and
- \( V \) is the volume.

### SI Units

1. **Mass**: The SI unit of mass is the kilogram (kg).
2. **Volume**: The SI unit of volume is the cubic meter (m³).

### SI Unit of Density

Given the definition of density, we can express it in terms of SI units:

\[
\text{Density} (\rho) = \frac{\text{Mass (kg)}}{\text{Volume (m}^3\text{)}}
\]

Therefore, the SI unit of density is:

\[
\text{kg/m}^3
\]

### Analyzing the Options

Now, let's evaluate the options provided:

(A) \( \text{g cm}^{-3} \) → This is a common unit for density but not the SI unit.

(B) \( \text{gm}^{-3} \) → This unit is not standard; it should be \( \text{g/m}^3 \), which is not the SI unit.

(C) \( \text{Kg m}^{-3} \) → This is equivalent to \( \text{kg/m}^3 \), which is indeed the SI unit of density.

(D) \( \text{Kg cm}^{-3} \) → This is also a common unit but not the SI unit.

### Conclusion

The correct answer is **(C) Kg m⁻³**.