What type of electromagnetic radiation is used in communications devices such as cellular telephones?

Radio waves is the type of electromagnetic radiation, which is used in communication devices such as cellular telephones.
Electromagnetic radiations are of many types which includes: Radio, Microwave, Infrared, Visible, Ultraviolet, X-rays and gamma rays, in which electric and magnetic field vary simultaneously. These rays or radiations are classified by wavelength.

Ithink d is the right answer. hope this !

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative.