Now, nuclear fission is a commonly occurring process for uranium 235, providing the identity of the missing daughter nuclide produced at the end of the reaction. All right, so we injected a neutron to uranium 235, which created uranium 236, which is unstable and it undergoes nuclear fission. We see the energy that's produced. We see one of the daughter products and we see our three neutrons being created.
Remember that your mass number, total mass number on both sides have to be the same and your total number of protons on both sides have to be the same. Here we have 236 on this reactant side here and we need 236 on the product side. Well, we have 141 here and then 3 * 1 is 3 so so far we have 144. What number do we need to have for A to also have a total mass number of 236? So 236 - 144 will give me 92, so here it would be 92.
And then if we look at the number of protons we have 92 on the reactant side here this is 0, so it doesn't contribute. Here we have 56. So if we do 92 - 56 here, that'll give me my number of protons as being equal to 36. If we look on the periodic table, what element has an atomic number 36 and be Krypton. So here this would be Krypton 92 which gives me option B as my correct answer.