Explanation:

- Resistivity is a property that quantifies how strongly a material opposes the flow of electric current.

- Option 1: $\mathrm{\Omega }$

- Ohm ($\mathrm{\Omega }$) is the SI unit for electrical resistance, not resistivity.

- Option 2: $\mathrm{\Omega }/\text{m}$

- This option suggests ohms per meter, which is not used for resistivity.

- Option 3: $\mathrm{\Omega }\text{ cm}$

- Ohm centimeter is used in some contexts but is not an SI unit.

- Option 4: $\mathrm{\Omega }\text{ m}$

- $\mathrm{\Omega }\text{ m}$ (ohm meter) is indeed the SI unit for resistivity.

Option 4: $\mathrm{\Omega }\text{ m}$ is the correct answer.