Question

Which of the following statements are correct?
(a) Lithium has the highest hydration enthalpy among the alkali metals.
(b) Lithium chloride is insoluble in pyridine
(c) Lithium can not form ethynide upon its reaction with ethyne.
(d) Both lithium and magnesium react slowly with $H_{2}O$

• A. (a), (b) and (d) only
• B. (b) and (c) only
• C. (a) and (d) only
• D. (a), (c) and (d) only

Answer 1

The correct option is D (a), (c) and (d) only

As the size of alkali metals decreases down the group, hydration enthalpy also decreases.
Solvation energy for lithium salt is higher than other alkali metal salts. So, $LiCl$ is soluble in pyridine.
Due to very high ionisation enthalpy of Li, it is the only alkali metal which does not lose electron and so can not react with ethyne to form ethynide.
Due to very small size and high hydration enthalpy, Li reacts less vigorously than other elements in the group.
Hence, (d) is the correct option.