(a) Differentiate between nuclear fission and fusion. (b) The fission properties of ${}_{94}\text{Pu}^{239}$ are very similar to those of ${}_{92}\text{U}^{235}$. How much energy (in MeV), is released if all the atoms in 1 g of pure ${}_{94}\text{Pu}^{239}$ undergo fission ? The average energy released per fission is 180 MeV.