A) Because the 2 missing electrons leave 2 protons without counterpart (the neutrons don;t matter at all here)
A, B, and C are all incorrect because they are talking about springs. I'm assuming you're talking about a 2 dimensional, side to side pendulum. In that case, the answer is D because as the pendulum goes up from one side, gravity accelerates it downward until it swings to the other side. If you're not talking about this type of pendulum, leave a comment and ill come back.
Mass always stays the same therefore it can’t be c and d. Volume stays the same because she is not removing anything. Therefore it is a