Can someone help me find the answer to this question? If possible, could you leave an explanation?
Thank you!

B. Radio Waves

Explanation:

There are several characteristics that show what kind of electromagnetic radiation you're dealing with. This graph they've provided you only shows wavelengths in the positive area (10^4 through 10^18). Every other choice they give you is either higher on the spectrum, or in the negative area.

Radio waves are at the front of the electromagnetic spectrum. They have the longest wavelength, lowest energy and lowest frequency. The graph below is something they should have showed you in the class and is the key to remembering each component of electromagnetic radiation and their properties.

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.

electric field is a function of 1/r^2

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