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NEET CHEMISTRYClassification of Elements and Periodicity in PropertiesMedium

Question

The sequence of ionic mobility in aqueous solution is:

A

K⁺ > Na⁺ > Rb⁺ > Cs⁺

B

Cs⁺ > Rb⁺ > K⁺ > Na⁺

C

Rb⁺ > K⁺ > Cs⁺ > Na⁺

D

Na⁺ > K⁺ > Rb⁺ > Cs⁺

Step-by-Step Solution

Ionic mobility in an aqueous solution depends on the size of the hydrated ion, not the gaseous ion radius.

  1. Hydration Concept: Smaller gaseous ions have a higher charge density and attract more water molecules, resulting in a larger hydrated radius. Conversely, larger gaseous ions have a smaller hydrated radius.
  2. Trends:
  • Gaseous Radii: Na+<K+<Rb+<Cs+Na^+ < K^+ < Rb^+ < Cs^+
  • Hydrated Radii: Na(aq)+>K(aq)+>Rb(aq)+>Cs(aq)+Na^+_{(aq)} > K^+_{(aq)} > Rb^+_{(aq)} > Cs^+_{(aq)}
  1. Mobility: Mobility is inversely proportional to the size of the moving species (the hydrated ion). Therefore, the smallest hydrated ion (Cs+Cs^+) moves the fastest, and the largest hydrated ion (Na+Na^+) moves the slowest.
  2. Conclusion: The order of ionic mobility is Cs+>Rb+>K+>Na+Cs^+ > Rb^+ > K^+ > Na^+. This is supported by conductivity data where λ0\lambda^0 for K+K^+ (73.5) is greater than Na+Na^+ (50.1) .

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Classification of Elements and Periodicity in Properties. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYClassification of Elements and Periodicity in Propertiessequencemobilityaqueoussolution

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A.$Ca^{2+} < K^+ < Ar < S^{2-} < Cl^-$
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