Chemistry question below?

Question

What is the oxidation numbers to the halogen in each of the following compound?

a) I2
b) ClO4-
c) HBrO3
d) Cl2O

Answer 1

a) 0 The ox # of an element is 0

b) 7+ O = [2- x 4] = 8- The entire polyatomic has a net charge of 1- . That means the Cl must have a 7+ ox #

c) 5+ H = 1+, O = [2- x 3 = 6-] This overall gives you 5- . The Br must be 5 +

d) 1+ O = 2- , 2 Cl = 2+ so 1 Cl must be 1+