Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): The Electromagnetic waves exert pressure on the surface on which they ar allowed to fall.

Reason (R): There is no mass associated with the electromagnetic waves.
In the light of the above statements,  Choose the correct answer from the options given below :

Assertion: EM waves carry energy ($$U$$) and momentum ($$p$$). For a completely absorbing surface, the momentum delivered is $$p = \frac{U}{c}$$. The rate of change of this momentum produces a net force. Therefore, EM waves do exert a physical pressure (radiation pressure) on any surface they strike. Hence, Assertion is true.

Reason: EM fields are configurations of energy, and their constituent particles (photons) possess zero rest mass. Hence, Reason is true.

EM waves exert pressure precisely because they carry linear momentum and energy, which can be transferred to a surface during a collision or absorption. The fact that they have no rest mass does not cause this pressure; rather, it highlights the unique relativistic property that a particle or wave can carry linear momentum ($$p = \frac{E}{c}$$) even when its rest mass is zero.

Since both statements are independently true but the Reason does not provide the causal explanation for the Assertion, the correct option is B.