Question

When potassium bromate (kbro3 ) is heated, it decomposes into potassium bromide and a gas that supports the combustion of a glowing splint?

Answer 1

We know that the oxygen (O2) causes a glowing splint to reignite, however, let us check what is missing on the products side of the chemical equation:
KBrO3 → KBr + ?
As we see, oxygen (O2) is the element missing from the other side. Therefore the balanced chemical equation for this decomposition is as follows:
2KBrO3 → 2KBr + 3O2