The static electric field inside a dielectric medium with relative permittivity, $\varepsilon _{r}=2.25$, expressed in cylindrical coordinate system is given by the following expression $$E=a_{r}2r+a_{\varphi }\left ( \frac{3}{r} \right )+a_{z}6$$ where $a_{r},a_{\varphi },a_{z}$ are unit vectors along $\text{r, $\varphi$ and z}$ directions, respectively. If the above expression represents a valid electrostatic field inside the medium, then the volume charge density associated with this field in terms of free space permittivity, $\varepsilon _{0}$ in $\text{SI}$ units is given by:
- $3\varepsilon _{0}$
- $4\varepsilon _{0}$
- $5\varepsilon _{0}$
- $9\varepsilon _{0}$