JEE PYQ: S Block Elements Question 3
Question 3 - 2021 (17 Mar Shift 1)
The correct order of conductivity of ions in water is:
(a) $\text{Na}^+ > \text{K}^+ > \text{Rb}^+ > \text{Cs}^+$ (b) $\text{Cs}^+ > \text{Rb}^+ > \text{K}^+ > \text{Na}^+$ (c) $\text{K}^+ > \text{Na}^+ > \text{Cs}^+ > \text{Rb}^+$ (d) $\text{Rb}^+ > \text{Na}^+ > \text{K}^+ > \text{Li}^+$
Show Answer
Answer: (b)
Solution
As the size of gaseous ion decreases, it gets more hydrated in water and hence the size of aqueous ion increases. When this bulky ion moves in solution, it experiences greater resistance and hence lower conductivity. Size of gaseous ion: $\text{Cs}^+ > \text{Rb}^+ > \text{K}^+ > \text{Na}^+$. Size of aqueous ion: $\text{Cs}^+ < \text{Rb}^+ < \text{K}^+ < \text{Na}^+$. Conductivity: $\text{Cs}^+ > \text{Rb}^+ > \text{K}^+ > \text{Na}^+$.
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