Match the LIST-I with LIST-II.
| LIST-I (Salt/ Complex in aqueous solution) | LIST-II (van't Hoff Factor) | ||
| A. | K2[HgI4] | I. | 7 |
| B. | Fe4[Fe(CN)6]3 | II. | 5 |
| C. | Mg3(PO4)2 | III. | 3 |
| D. | Na3PO4 | IV. | 4 |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-III, B-I, C-II, D-IV
The van’t Hoff factor, i, for a strong electrolyte that dissociates completely is the number of ions given by one formula unit. A complex ion (in square brackets) does not break up; it counts as one ion.
A. \( \ce{K2[HgI4]} \) — This matches III. 3. It gives two \( \ce{K^{+}} \) ions and one complex anion.
\( \displaystyle \ce{K2[HgI4] -> 2K^+ + [HgI4]^2-},\quad i=2+1=3 \)
B. \( \ce{Fe4[Fe(CN)6]3} \) — This matches I. 7. It gives four \( \ce{Fe^{3+}} \) ions and three hexacyanidoferrate(II) ions.
\( \displaystyle \ce{Fe4[Fe(CN)6]3 -> 4Fe^3+ + 3[Fe(CN)6]^4-},\quad i=4+3=7 \)
C. \( \ce{Mg3(PO4)2} \) — This matches II. 5. It gives three \( \ce{Mg^{2+}} \) ions and two phosphate ions.
\( \displaystyle \ce{Mg3(PO4)2 -> 3Mg^2+ + 2PO4^3-},\quad i=3+2=5 \)
D. \( \ce{Na3PO4} \) — This matches IV. 4. It gives three \( \ce{Na^{+}} \) ions and one phosphate ion.
\( \displaystyle \ce{Na3PO4 -> 3Na^+ + PO4^3-},\quad i=3+1=4 \)
Shortcut: A–III appears only in Options (3) and (4), and B–I then leaves only Option (3).