If the magnetic field intensity $(H)$ in a conducting region is given by the expression. $H = x^{2} \hat{i} + x^{2}y^{2}\hat{j} + x^{2}y^{2}z^{2}k$ $\text{A/m}$. The magnitude of the current density, in $A/m^{2}$, at $x = 1\;m, y = 2\; m$ and $z = 1\; m$, is

- $8$
- $12$
- $16$
- $20$