Question

what is the oxidation state of chlorine in NaClO3?

Answer 1

So...
Oxygen usually has an oxidation state of -2
Sodium always have an oxidation state of +1
Now, chlorine... It usually have oxidation state of -1, but it can be oxidized further if the neighboring atoms is more electronegative than itself (the oxygen).

Knowing that the compound is neutral, you can rationalize that the chlorine has to be oxidized to keep the whole thing 0, but what? Count all the formal charges the other known atoms have, so: +1 + 3(-2) = -5. So in order to keep the whole thing neutral, chlorine has to be +5