What are the oxidation numbers of all atoms in PH4+?

Answer 1

P = -3 and H = +1

Do not forget that H always has an oxidation state of 1+ except when in metal hydrides

Answer 2

PH₄⁺

For Hydrogen

Each H is +1

4 x 1+ = 4+

For Phosphorus

By doing some algebra, you can find that PH₄⁺

P needs to be 3- because the overall charge of the PH₄⁺ is 1+

overall = hydrogen + phosphorus

(1+) = (4+) + (3-)