Question

Which one of the following alkali metals gives hydrated salts?

• A. $\mathrm{K}$
• B. $\mathrm{Li}$
• C. $\mathrm{Na}$
• D. $\mathrm{Cs}$

Answer 1

The correct option is B

$\mathrm{Li}$

Explanation for correct option

(B) $\mathbf{Li}$

Hydration energy

• Enthalpy of hydration is defined as the amount of energy released upon dilution of one mole of gaseous ions.
• Its values are usually negative and it is also known as hydration energy.
• The hydration enthalpy will be larger for smaller ions because they can fit more water molecules around them and get hydrated.
• Due to the atom's size increasing as a result of the more valence shells added, hydration enthalpy decreases along with the group.

Order of hydration energy in alkali metals

• Lithium $\left(\mathrm{Li}\right)$ is the smallest alkali metal in size.
• It has the highest hydration energy among all alkali metals.
• The order of hydration energy is as follows:

$\mathrm{Li}>\mathrm{Na}>\mathrm{K}>\mathrm{Rb}>\mathrm{Cs}$

• Lithium's high charge density is another characteristic that gives the metal high hydration energy.
• As a result, Lithium can form hydrated salt.

Explanation for incorrect options

• Lithium gives hydrated salts.
• Hence, all other options (A), (C) and (D) are incorrect.

Therefore, the correct option is (B) $\mathbf{Li}$.