Question: Which sort of atom would require more energy to split in a fission reaction, 
 Option1: Helium, with its two protons 
 Option2: Plutonium, with its 94 protons? 
 Explanation: As more protons are added to the nucleus, the electromagnetic force of repulsion between them gets stronger, while the strong nuclear force of attraction between them gets weaker.
Helium, with its two protons