Which of the following electromagnetic waves is not used for communication?
a gamma rays
b microwaves
c infrared waves
d radio waves

Microwaves and radio waves are employed in radio and satellite communications while infrared waves are used in remote controls and infrared features of new phones and other electrons. However, gamma rays have far too much energy and cause damage to the body. They are not used in communication.
The answer is A.

An atom that has fewer electrons that protons is called a positive ion.