JEE Main 2025 Apr 3 Shift 1, Chemistry Q20: Colligative Properties

Standard limiting molar conductivities at 298 K (S cm${}^2$ mol${}^{-1}$):

${\text{H}}^{+}\approx 349.8$ (anomalously high due to the Grotthuss proton-hopping mechanism)

${\text{Ca}}^{2+}\approx 119$, ${\text{Mg}}^{2+}\approx 106$ (divalent, two charges contribute)

${\text{K}}^{+}\approx 73.5$, ${\text{Na}}^{+}\approx 50.1$ (Na${}^{+}$ is more strongly hydrated, larger hydrated radius, lower mobility than K${}^{+}$)

$\therefore$ Order: ${\text{H}}^{+}>{\text{Ca}}^{2+}>{\text{Mg}}^{2+}>{\text{K}}^{+}>{\text{Na}}^{+}$.