9. Which wave on the electromagnetic spectrum has the longest wavelength
and lowest frequency? What are these waves used for

Radio Waves have the longest wavelength therefore they have the lowest frequency.

Radio waves are typically used in your everyday electrical appliances, such as TVs, phones, ovens, microwaves, and more. They are also used in radio towers in order to send a message across or when your listening to the radio. They help bring the music to you when you are using the radio.

i think the answer is a, hope this : )