Which of the following ions is in the lowest oxidation state?

C. Fe in Fe₂O₃

Explanation:

The sum of the oxidations states times the atomicity is equal to the charge of the molecule.

A.

2.H + 1.P + 4.O = -1

2.(1+) + 1.P + 4.(2-) = -1

P = +5

B.

2.Cr + 7.O = -2

2.Cr + 7.(-2) = -2

2.Cr = 12

Cr = +6

C.

2.Fe + 3.O = 0

2.Fe + 3.(-2) = 0

2.Fe = 6

Fe = +3

Fe has the lowest oxidation state (+3).

your parents i think this could be it