If 2.5 x 1018 particles of KClO3 breaks down, how many formula units of potassium chloride (KCl) will form?

Answer 1

The balanced equation is shown below

2KClO₃(s)=2KCl(s)+3O₂(g)

so the mole ratio between the KClO₃(s) and KCl(s) is 1:1

Thus you have the same number of particles of KCl as the number you started with before the reaction.