Phosphorus in Different Acids and its Oxidation State

Phosphorus Acid (H3PO3)
- In phosphorous acid (H3PO3), phosphorus is present in the +3 oxidation state.
- The formula of phosphorous acid is H3PO3, which suggests that it contains three hydrogen atoms and three oxygen atoms.
- The oxidation state of hydrogen is always +1 and oxygen is usually -2.
- By using these oxidation states, we can calculate the oxidation state of phosphorus in phosphorous acid.
- Let x be the oxidation state of phosphorus.
- The sum of the oxidation states of all the atoms in a neutral molecule is zero.
- Therefore, 3(+1) + x + 3(-2) = 0
- Simplifying the equation gives 3 + x - 6 = 0
- Solving for x, we find x = +3.
- Hence, the oxidation state of phosphorus in phosphorous acid is +3.

Orthophosphoric Acid (H3PO4)
- Orthophosphoric acid (H3PO4) is a stronger acid than phosphorous acid.
- In orthophosphoric acid, the oxidation state of phosphorus is +5.
- Just like before, let x be the oxidation state of phosphorus.
- The sum of the oxidation states of all the atoms in a neutral molecule is zero.
- Therefore, 3(+1) + x + 4(-2) = 0
- Simplifying the equation gives 3 + x - 8 = 0
- Solving for x, we find x = +5.
- Hence, the oxidation state of phosphorus in orthophosphoric acid is +5.

Hypophosphorous Acid (H3PO2)
- Hypophosphorous acid (H3PO2) is a weaker acid than phosphorous acid.
- In hypophosphorous acid, the oxidation state of phosphorus is +1.
- Just like before, let x be the oxidation state of phosphorus.
- The sum of the oxidation states of all the atoms in a neutral molecule is zero.
- Therefore, 3(+1) + x + 2(-2) = 0
- Simplifying the equation gives 3 + x - 4 = 0
- Solving for x, we find x = +1.
- Hence, the oxidation state of phosphorus in hypophosphorous acid is +1.

Metaphosphoric Acid (HPO3)
- Metaphosphoric acid (HPO3) is an acid with a polymeric structure.
- In metaphosphoric acid, the oxidation state of phosphorus is +5.
- Just like before, let x be the oxidation state of phosphorus.
- The sum of the oxidation states of all the atoms in a neutral molecule is zero.
- Therefore, x + 3(-2) = 0
- Simplifying the equation gives x - 6 = 0
- Solving for x, we find x = +6.
- Hence, the oxidation state of phosphorus in metaphosphoric acid is +5.

Therefore, the correct answer is option 'A' as phosphorus has an oxidation state of +3 in phosphorous acid.