A) \[{{K}^{+}}>N{{a}^{+}}>R{{b}^{+}}>C{{s}^{+}}\]
B) \[C{{s}^{+}}>R{{b}^{+}}>{{K}^{+}}>N{{a}^{+}}\]
C) \[R{{b}^{+}}>{{K}^{+}}>C{{s}^{+}}>N{{a}^{+}}\]
D) \[N{{a}^{+}}>{{K}^{+}}>R{{b}^{+}}>C{{s}^{+}}\]
Correct Answer: B
Solution :
Key Idea: The smaller the size of ion, the greater the degree of hydration and Mobility of ion in aqueous solution \[\propto \frac{\text{1}}{\text{size of ion in aqueous solution}}\] Generally in a group size or radii of ions increases, so Li has smallest size thus bind maximum number of water molecules with itself and becomes largest in size (in aqueous solution). Hence, the order of ionic radii (size) of alkali metal ions in aqueous solution is \[L{{i}^{+}}>N{{a}^{+}}>{{K}^{+}}>R{{b}^{+}}>C{{s}^{+}}\] Thus, the order of mobility \[C{{s}^{+}}>R{{b}^{+}}>{{K}^{+}}>N{{a}^{+}}>L{{i}^{+}}\]
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