Match the List-I with List-II:
A. Microwaves   I. Radioactive decay of the nucleus
B. Gamma rays   II. Rapid acceleration and deceleration of electron in aerials
C. Radio waves   III. Inner shell electrons
D. X-rays   IV. Klystron valve

Let us match each type of electromagnetic wave with its source:

A. Microwaves - Microwaves are produced using a Klystron valve (IV), which is a specialized vacuum tube used for generating and amplifying microwaves.

B. Gamma rays - Gamma rays are produced by Radioactive decay of the nucleus (I). When an unstable nucleus transitions from a higher energy state to a lower energy state, it emits gamma radiation.

C. Radio waves - Radio waves are produced by the Rapid acceleration and deceleration of electrons in aerials (II). Oscillating charges in an antenna produce radio waves.

D. X-rays - X-rays are produced by transitions of Inner shell electrons (III). When inner shell electrons are knocked out and outer electrons fill the vacancy, characteristic X-rays are emitted.

Therefore, the correct matching is: A-IV, B-I, C-II, D-III.