The correct option is Pascal.
Explanation
Pressure is defined as the force applied perpendicular to the surface of an object per unit area. In the International System of Units (SI), derived units are constructed from the seven base units to measure such physical quantities.
- Pascal (Pa): This is the SI derived unit of pressure. It is defined as one newton per square meter ($1 \text{ Pa} = 1 \text{ N} \cdot \text{m}^{-2}$). It is named after the physicist Blaise Pascal.
- Bar: This is a metric unit of pressure commonly used in meteorology, defined as exactly $10^5 \text{ Pa}$. However, it is not an SI unit.
- Torr: This is a non-SI unit defined as $1/760$ of a standard atmosphere. It is historically related to the pressure exerted by one millimeter of mercury (mmHg).
- Atmosphere (atm): This is a non-SI reference unit equal to $101,325 \text{ Pa}$, representing the average atmospheric pressure at sea level.
Key Takeaway: While units like Bar, Torr, and Atmosphere are frequently used in scientific contexts, the Pascal (Pa) is the sole official SI derived unit for pressure.