What is oxidation number of P in P(OH)3?

The oxidation number of phosphorus (P) in ( \text{P(OH)}_3 ) is +3. This is because each hydroxide ion (( \text{OH}^- )) carries a -1 charge, and the overall compound must be electrically neutral. Since there are 3 hydroxide ions each with a -1 charge, phosphorus must have a +3 oxidation number to balance the charges.