JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Redox Reactions and Electrochemistry

The correct order of conductivity of ions in water is:

(A) $Rb^{+} > Na^{+} > K^{+} > Li^{+}$
(B) $Cs^{+} > Rb^{+} > K^{+} > Na^{+}$ ✓ Correct
(C) $K^{+} > Na^{+} > Cs^{+} > Rb^{+}$
(D) $Na^{+} > K^{+} > Rb^{+} > Cs^{+}$

Answer: (B)

Solution

The conductivity of an ion in water is set by how fast it moves, and that depends on the size of the hydrated ion rather than the bare ion. A smaller bare cation has the higher charge density, binds more water molecules and so drags a bulkier hydration sphere. Among the alkali metal ions the bare radius grows from

N a^{+}

C s^{+}

while the hydrated radius shrinks in the same direction, so mobility and conductivity rise from

N a^{+}

C s^{+}

. The correct order is

C s^{+} > R b^{+} > K^{+} > N a^{+}

JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Redox Reactions and Electrochemistry

Solution

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