JEE Main 2021 · 16 March · morning · Single correct · +4 / −1
Match List - I with List - II :
Choose the correct answer from the options given below :
| List - I Name of oxo acid | List - II Oxidation state of 'P' | ||
|---|---|---|---|
| (a) | Hypophosphorous acid | (i) | +5 |
| (b) | Orthophosphoric acid | (ii) | +4 |
| (c) | Hypophosphoric acid | (iii) | +3 |
| (d) | Orthophosphorous acid | (iv) | +2 |
| (v) | +1 |
- (a) (a) - (iv), (b) - (v), (c) - (ii), (d) - (iii)
- (b) (a) - (iv), (b) - (i), (c) - (ii), (d) - (iii)
- (c) (a) - (v), (b) - (i), (c) - (ii), (d) - (iii)
- (d) (a) - (v), (b) - (iv), (c) - (ii), (d) - (iii)
Answer and solution
Answer (c) (a) - (v), (b) - (i), (c) - (ii), (d) - (iii)
Solution
Chemistry ma’am · 3 steps
Write the formula of each acid first, then the oxidation state of P is just one line of algebra.
- Know the formulae. Hypophosphorous acid is H₃PO₂, orthophosphoric acid is H₃PO₄, hypophosphoric acid is H₄P₂O₆ and orthophosphorous acid is H₃PO₃.
- Set up the sum. Take H as +1 and O as -2, and set the total to zero. This works even for the P–H bonds in H₃PO₂ and H₃PO₃, because H still counts as +1.
Acid Formula Working Oxidation state of P Hypophosphorous H₃PO₂ 3 + x - 4 = 0 +1 (v) Orthophosphoric H₃PO₄ 3 + x - 8 = 0 +5 (i) Hypophosphoric H₄P₂O₆ 4 + 2x - 12 = 0 +4 (ii) Orthophosphorous H₃PO₃ 3 + x - 6 = 0 +3 (iii) - So. The match is (a)–(v), (b)–(i), (c)–(ii), (d)–(iii), which is option (c).
The idea to keep. For any oxoacid of phosphorus, write the formula and balance H = +1, O = −2 to zero. In a dimer like H₄P₂O₆, remember to divide by the two P atoms.
Answer from the NTA final answer key. Solution by PrepWiser.