Among the statements (A)-(D), the correct ones are :
(a) Lithium has the highest hydration enthalpy among the alkali metals.
(b) Lithium chloride is insoluble in pyridine.
(c) Lithium cannot form ethynide upon its reaction with ethyne.
(d) Both lithium and magnesium react slowly with $H_2O$ .
Lithium has highest hydration enthalpy among alkali metals due to its small size.LiCl is soluble in pyridine because LiCl have more covalent character.Li does not form ethynide with ethyne. Both Li and Mg reacts slowly with $H_{2}O$