Question

How many moles of oxygen will be produced from the decomposition of 3 moles of `KClO_3` in the reaction `KClO_3 -> KCl + O_2`?

Answer 1

We first have to balance the equation, because it isn't.

Explanation:

`KClO_3>KCl+1 1/2 O_2` because there are three `O`'s

Or rather:
`2KClO_3->2KCl+3 O_2`

This doesn't matter for the solution because every mole of `KClO_3` will produce `1 1/2` mole of `O_2`

You can do the last bit.