Here it says to identify the energetic particle in the following nuclear reaction. In this nuclear reaction we have thorium 231. It's going to decompose and it gives us a new isotope. So here this is protactinium 231 and it gives us this element here or this notation.
Here we have an E which stands for electron and -1. So this electron represents our energetic particle. It is on the product side. But remember, when it comes to energetic particles, they can appear in either the reactant side or the product side. You've got to keep an eye out for them, OK?
In this example, this represents our energetic particle.