Given below are two statements: one is labelled as Assertion (A)...

Assertion (A) is true: The dimensional formula of pressure is $P = \dfrac{\text{Force}}{\text{Area}} = \dfrac{[\text{MLT}^{-2}]}{[\text{L}^2]} = [\text{ML}^{-1}\text{T}^{-2}]$.
Energy density is energy per unit volume, so its dimensional formula is $u = \dfrac{\text{Energy}}{\text{Volume}} = \dfrac{[\text{ML}^2\text{T}^{-2}]}{[\text{L}^3]} = [\text{ML}^{-1}\text{T}^{-2}]$.
Thus, pressure and energy density have the same dimensional formula.

Reason (R) is false: Energy density is defined as the energy stored per unit volume, not as force acting per unit area (which is the definition of pressure). Although they are dimensionally equivalent, their physical definitions are entirely different.

Answer: Assertion (A) is true but Reason (R) is false.