Write the $SI$ unit of resistivity.

(A) The $SI$ unit of resistivity is the ohm-metre, denoted as $\Omega \cdot m$.
Resistivity $(\rho)$ is defined by the formula $R = \rho \frac{l}{A}$, where $R$ is resistance, $l$ is length, and $A$ is the cross-sectional area.
Rearranging for resistivity gives $\rho = \frac{R \cdot A}{l}$.
Substituting the $SI$ units: $\Omega \cdot \frac{m^2}{m} = \Omega \cdot m$.