Among the statements $\left(\mathrm{a}\right)-\left(\mathrm{d}\right),$ the correct ones are:
$\left(\mathrm{a}\right)$ Lithium has the highest hydration enthalpy among the alkali metals.
$\left(\mathrm{b}\right)$ Lithium chloride is insoluble in pyridine.
$\left(\mathrm{c}\right)$ Lithium cannot form ethynide upon its reaction with ethyne.
$\left(\mathrm{d}\right)$ Both lithium and magnesium react slowly with ${\mathrm{H}}_2\mathrm{O}$ .