Solution:

The dielectric constant (also called the relative permittivity, $\varepsilon_r$) is a dimensionless quantity because it is defined as the ratio:

$$\varepsilon_r = \frac{\varepsilon}{\varepsilon_0}$$

Where:

• $\varepsilon$ = permittivity of the medium (units: $\text{F/m}$, farads per meter)
• $\varepsilon_0$ = permittivity of free space ($\text{F/m}$, farads per meter)

Since it is a ratio of two quantities with the same unit, the dielectric constant has no unit (it is dimensionless).