Explanation

J/m² (joule per square metre) is the unit of surface tension / energy per unit area — not of pressure. The pascal (Pa), which is identically N/m² (newton per square metre), is the SI unit of pressure, and the bar is a widely used non-SI unit of pressure (1 bar = 10⁵ Pa). Hence J/m² is the one that is not a unit of pressure — option C.