What are the oxidation numbers of K, Cl, and O in KClO3?

Question

A. K = +2, Cl = +4 and O = –2

B. K = +1, Cl = +5 and O = –2

C. K = +3, Cl = +3 and O = –2

D. K = +1, Cl = –5 and O = –2

E. None of the Above

Answer 1

KClO₃

K is in group 1 of the periodic table so ON = +1

O always has an ON = -2 except in peroxides when it is -1

Cl can have variable ONs so we must figure it out.

If K is +1 and O is -2, and there are 3 Oxygens, so that we have +1 and -6. That's a net of -5. So Cl must be +5 in order for KClO3 to be neutral (have zero charge)

Answer: K = +1, Cl = +5, O = -2 (Choice B)