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JEE Main levelSingle correct optionDifficulty 2 of 3ec08

The correct order of limiting molar ionic conductivities in water at 298 K is

A $Li X^{+} > Na X^{+} > K X^{+}$
B $K X^{+} > Na X^{+} > Li X^{+}$
C $Na X^{+} > K X^{+} > Li X^{+}$
D $Li X^{+} = Na X^{+} = K X^{+}$

Answer: B

The smaller bare ion has the larger hydration shell. The hydrated radius order is

Li X^{+} > Na X^{+} > K X^{+}

, so mobility and ionic conductivity run the other way:

K X^{+} (73.5) > Na X^{+} (50.1) > Li X^{+} (38.7) S c m^{2} mo l^{- 1}

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