So here in this example question that says label each reaction as chemical or nuclear. Remember in chemical reactions the identity of elements stay the same on both sides, but for a nuclear reaction our elements change identity because we have a changing of the number of protons.

If we take a look at the first one, we're starting out with oxygen 15 and if we look on the other side, oxygen is nowhere to be found. Instead we have fluorine 15 and we actually have a positron. Here the identity of our reactants changed, so this would represent a nuclear reaction.

For our second reaction, we have two magnesium atoms combining with one oxygen molecule to produce two magnesium oxide compound. Here we're going to say we have two magnesiums on both sides and two oxygens on both sides. The identity of our elements have not changed, so this is a chemical reaction or regular reaction.

So this is how we'd identify both of these reactions given to us in this example question.