The oxidation state of phosphorus is +3 in
a) orthophosphoric acid b) phosphorus acid
c) metaphosphoric acid d) phyrophosphoric acid

b) Phosphorus acid

Explanation:

To distinguish the type of acid of phosphorus with the oxidation state of +3, we need to be familiar with the chemical formula of each of the compounds:

    Orthophosphoric acid             H₃PO₄

    Phosphorus acid                       H₃PO₃

    Metaphosphoric acid               HPO₃

    Phyrophosphoric acid               H₄P₂O₇

Now that we know the formula of the given compounds, the algebraic sum of all the oxidation numbers of all atoms in a neutral compound is zero:

Only phosphorus acid yielded an oxidation state of +3 for phosphorus in the compound.

  H₃PO₃:

   we know the oxidation state of H = +1

                                                          O = -2

         The oxidation state of P is unknown. We can express this as an equation:

                3(+1) + P + 3(-2) = 0

                    3 + P -6 = 0

                          P-3 = 0

                          P = +3

< > according to newton's third law of motion, forces always act in equal but opposite pairs. another way of saying this is for every action, there is an equal but opposite reaction.< >