JEE MAIN - Chemistry (2025 - 3rd April Morning Shift - No. 18)
Correct order of limiting molar conductivity for cations in water at 298 K is :
$\mathrm{H}^{+}>\mathrm{Na}^{+}>\mathrm{K}^{+}>\mathrm{Ca}^{2+}>\mathrm{Mg}^{2+}$
$\mathrm{H}^{+}>\mathrm{Ca}^{2+}>\mathrm{Mg}^{2+}>\mathrm{K}^{+}>\mathrm{Na}^{+}$
$\mathrm{Mg}^{2+}>\mathrm{H}^{+}>\mathrm{Ca}^{2+}>\mathrm{K}^{+}>\mathrm{Na}^{+}$
$\mathrm{H}^{+}>\mathrm{Na}^{+}>\mathrm{Ca}^{2+}>\mathrm{Mg}^{2+}>\mathrm{K}^{+}$
Explanation
The limiting molar conductivities of ions are important in determining how well they conduct electricity in solution. Here are the values for some common cations at 298 K:
H⁺: 349.8 S cm² mol⁻¹
Na⁺: 50.11 S cm² mol⁻¹
K⁺: 73.52 S cm² mol⁻¹
Ca²⁺: 119 S cm² mol⁻¹
Mg²⁺: 106.12 S cm² mol⁻¹
Based on these values, the correct order of limiting molar conductivity for these cations is:
$ \stackrel{\oplus}{\text{H}}^+ > \text{Ca}^{2+} > \text{Mg}^{2+} > \text{K}^+ > \text{Na}^+ $
This order reflects the decreasing ability of each ion to conduct electricity in water under the given conditions.
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