$$X$$-rays and $$\gamma$$-rays of same energies are distinguished by their:
Method of production
The correct option is D Method of production
The $$X$$-rays and the $$\gamma$$-rays of the same energy cannot be distinguished from one another by frequency method as the frequency of a wave is the property of its energy. They both will have the same frequency and energy.
The charge and the ionization power of the waves will also depend on the energy and frequency of the wave.
But the two waves will always have different methods of production. So, they can be differentiated by their method of production.