Question

Which wave property is directly proportional to its energy of electromagnetic radiation?

Answer 1

It the frequency of the EM wave

Each quantum of radiant energy, E=hν, where h=Plank's constant and ν=frequency of EM wave.

Answer 2

electromagnetic radiation :- it is a kind of radiation in which electric and magnetic field vary simultaneously. electromagnetic radiation follows quantum theory.
so, energy radiant by electromagnetic radiation in a small package e.g., photon. energy of each photon , $E=h\nu$
where h is plank's constant and $\nu$ frequency of radiant electromagnetic wave.

hence , here it is clear that energy of electromagnetic radiation is directly proportional to frequency of it.