What do radio waves and gamma rays have in common?
a - they are both electromagnetic waves.
b - they are both low frequency waves.
c - they can only travel in a vacuum.
d - they both are part of the visible light spectrum

A - They are both electromagnetic waves.

Explanation:

Electromagnetic waves are waves consisting of periodic oscillations of electric and magnetic fields, that vibrate in a plane perpendicular to the direction of propagation of the wave (for this reason, they are said to be "transverse waves").

Electromagnetic waves, unlike mechanical waves, can travel through a vacuum, and do not need a medium to propagate. Their speed in a vacuum is a constant and it is called speed of light ().

Electromagnetic waves are classified, depending on their wavelength and frequency, into 7 different types - together they form the electromagnetic spectrum. The 7 types, listed from shortest to longest wavelength, are:

gamma rays

X-rays

ultraviolet radiation

visible light

infrared radiation

microwaves

radio waves

All these waves, despite having different properties, are all electromagnetic waves -so we see that both radio waves and gamma rays belong to this type of waves.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.