Question

what is the oxidation number of Cl in ClO3-

Answer 1

Cl = ??
O has oxidation number -2 and you have 3 so 3(-2) = -6
but you see the ClO3 has an oxidation of -1

s0

-6 + ( the oxidation of Cl) = -1

Answer 2

No, sorry, that is not correct, please review the calculations,
-6 - (-1) = ?
the oxidation of Cl it is not -1 in ClO3-

Answer 3

no it is +5

see

-6+ 5 -=-1

Answer 4

-6 + (what is the oxidation of Cl) = -1