The substance having the same value of van't Hoff factor as that of \(K_4[Fe(CN)_6]\) is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Al2(SO4)3
The van’t Hoff factor i is the number of particles one formula unit gives in solution. For a strong electrolyte that dissociates completely, i equals the number of ions:
\( \displaystyle \ce{K4[Fe(CN)6] -> 4K+ + [Fe(CN)6]^4-}\qquad i = 4 + 1 = 5 \)
\( \displaystyle \ce{Al2(SO4)3 -> 2Al^3+ + 3SO4^2-}\qquad i = 2 + 3 = 5 \)
Both give five ions, so they have the same van’t Hoff factor.
Option (1) AlCl3 — Incorrect. \( \ce{AlCl3 -> Al^3+ + 3Cl-} \), so i = 1 + 3 = 4.
Option (2) AlN — Incorrect. Aluminium nitride is a hard covalent solid that does not dissolve as ions; even as \( \ce{Al^3+} \) + \( \ce{N^3-} \) it would give only i = 2.
Option (3) AlF3 — Incorrect. \( \ce{AlF3 -> Al^3+ + 3F-} \), so i = 1 + 3 = 4.
NCERT (2026-27 edition):
Abnormal Molar Masses – …
