Part of a radioactivity decay series is represented below. It involves the change of a nucleus M into a nucleus N by the emission of a beta-particle, followed by a further change into a nucleus Q by the emission of an alpha particle. Four quantities V, W, X and Y are shown What are the expressions for X and Y?

Answer:

19) G

When a ß-paricle is emitted, an electron is emitted. This means that the proton number (atomic number) increases by 1. The mass number DOES NOT change when a ß-particle is emitted.
Therefore, X = W+1

When an α-particle is emitted, a Helium atom is emitted. This means that the mass number decreases by 4 and the atomic number decreases by 2.
So, Y = V-4

So the answer is G.