Oxidation number??? HELP?

(a)
ClO₄¹⁻ (Cl underlined)
For multi-atomic ion: Total oxidation numbers = Charge of the ion
(Oxidation number of Cl) + (Oxidation number of O) × 4 = -1
(Oxidation number of Cl) + (-2) × 4 = -1
Oxidation number of Cl = +7


(b)
ClO₂¹⁻ (Cl underlined)
For multi-atomic ion: Total oxidation numbers = Charge of the ion
(Oxidation number of Cl) + (Oxidation number of O) × 2 = -1
(Oxidation number of Cl) + (-2) × 2 = -1
Oxidation number = +3


(c)
NH₃ (N underlined)
For neutral compound: Total oxidation number = 0
(Oxidation number of N) + (Oxidation number of H) × 3 = 0
(Oxidation number of N) + (+1) × 3 = 0
Oxidation number of N = -3


(d)
ClO¹⁻ (Cl underlined)
For multi-atomic ion: Total oxidation numbers = Charge of the ion
(Oxidation number of Cl) + (Oxidation number of O) = -1
(Oxidation number of Cl) + (-2) = -1
Oxidation number = +1


(e)
Actually, H₃PO does not exist.

If it is H₃PO₄ (P underlined)
For neutral compound: Total oxidation number = 0
(Oxidation number of H) × 3 + (Oxidation number of P) + (Oxidation number of O) × 4 = 0
(+1) × 3 + (Oxidation number of P) + (-2) × 4 = 0
Oxidation number of P = +5

If it is H₃PO₃ (P underlined)
For neutral compound: Total oxidation number = 0
(Oxidation number of H) × 3 + (Oxidation number of P) + (Oxidation number of O) × 3 = 0
(+1) × 3 + (Oxidation number of P) + (-2) × 3 = 0
Oxidation number of P = +3