<span>Each color has a different wavelength allowing the eye to see it.</span>
The best and most correct answer among the choices provided by the question is the fourth choice. The phenomenon that Michael Faraday explored was electricity and magnetism. I hope my answer has come to your help. God bless and have a nice day ahead!
Answer:
Part a)

Part b)

Explanation:
Part a)
As we know that both charge particles will exert equal and opposite force on each other
so here the force on both the charges will be equal in magnitude
so we will have

here we have

now we have

Part b)
Now for the force between two charges we can say

now we have

now we have

The answer is earth's crust