Question

Missing item would complete this alpha decay reaction? `"_98^251Cf` `->``"_96^247Cm + ?`

Answer 1

If you recall that conservation of mass dictates that the atomic number and mass number must add up on both sides to be equal, you should find that

`""_(2)^(4) X`

is missing. That means the mass number is `4` and the atomic number is `2`. That is the helium atom. More specifically, it is `""_2^4 "He"`, which is Helium-4.