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Answer & exp.

Explanation:

Some Rules Regarding Oxidation Numbers:

- Hydrogen has oxidation number of + 1 except in hydrides where it is -1

- Oxygen has oxidation number of -2 except in peroxides where it is -1

- Some elements have fixed oxidation numbers. E.g Halogen group elements has oxidation number of -1

- Oxidation number of a compound is the sum total of the individual elements and a neutral  compound has oxidation number of 0.

A. HI

Hydrogen has oxidation of + 1

Oxidation number of I:

1 + x = 0

x = -1

B. PBr3

Br has oxidation number of - 1

Oxidation number of Pb:

x + 3 (-1) = 0

x = + 3

C. KH

Hydrogen has oxidation of + 1

Oxidation number of K:

1 + x = 0

x = -1

D. H3PO4

Hydrogen has oxidation number of + 1

Oxygen has oxidation number of -2

Oxidation number of P:

3(1) + x + 4(-2) = 0

3 + x - 8 =0

x = 5

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