The answer is A. It shows a nuclear type of reaction, specifically nuclear fission reaction. Nuclear fission is the splitting of heavy nucleus into lighter nuclei. Large energies from nuclear reactions are due to the process of splitting the atoms apart. The bonds that keep together the parts of an atom has much higher energies than the chemical bonds in a molecule about a million times. Thus, when you try splitting the parts of an atom these energies are released which may cause an explosion when not properly handled.
