1. Tardigrade
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  3. Chemistry
  4. Consider the following abbreviations for hydrated alkali ions X=[Li(H2 O)n]+ Y=[K(H2 O)n]+ Z=[ Cs (H2 O)n]+What is the correct order of size of these hydrated alkali ions?

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Q. Consider the following abbreviations for hydrated alkali ions $X=\left[Li\left(H_{2} O\right)_{n}\right]^{+}$ $Y=\left[K\left(H_{2} O\right)_{n}\right]^{+} Z=\left[ Cs \left(H_{2} O\right)_{n}\right]^{+}$What is the correct order of size of these hydrated alkali ions?

J & K CETJ & K CET 2006

Solution:

All alkali metal salts are soluble in water. The degree of hydration depends upon the size of the cation. Smaller the size of a cation, greaten is its charge density and hence, greater is its tendency to withdraw electrons molecules which are thus polarised. $ Li^{+} $ ion being smallest in size among alkali metal ions is the most extensively hydrated while $ Cs^{+} $ ion the largest alkali metal ion is the least hydrated. The size of hydrated alkali ions is as
$ Li^{+} > Na^{+} > K^{+} > Rb^{+} > Cs^{+} $
(Relative ionic radii in water) (Relative degree of hydration)