Dioptre is the unit of :

A dioptre (symbol: D) is the SI unit of measurement for the optical power of a lens or curved mirror. It is defined as the reciprocal of the focal length (f) measured in metres (P = 1/f). Therefore, 1 dioptre is equal to 1 m^-1. A convex lens has positive power, while a concave lens has negative power.

• Diffusion rate: This refers to the amount of substance diffusing per unit area per unit time, typically measured in mol/m²·s.
• Dipole moment: The electric dipole moment is measured in Coulomb-metres (C·m) or Debye (D). While both use 'D', the question specifically names "Dioptre".
• Intensity of light: Luminous intensity is measured in candela (cd), which is an SI base unit.