Pressure is defined as force acting per unit area ($P = F/A$).

1. SI Unit: The SI unit of force is the Newton ($N$) and area is the square metre ($m^2$). Therefore, the SI unit of pressure is Newton per square metre ($N m^{-2}$).
2. Naming: This unit ($N m^{-2}$) has been named as the pascal (Pa) in honour of the French scientist Blaise Pascal .
3. Other Options:

• Dynes/cm²: This corresponds to the CGS system of units.
• Atmosphere (atm): A common unit for measuring pressure, especially in fluids, but not the SI unit ($1 \text{ atm} = 1.013 \times 10^5 \text{ Pa}$) .
• cm of Hg: A unit based on the hydrostatic pressure exerted by a column of mercury, used in manometers and barometers .