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 ${\mathrm{H}}_2\mathrm{O}$ .

• A

  $\left(\mathrm{a}\right),\mathrm{}\left(\mathrm{b}\right)$ and $\left(\mathrm{d}\right)$ only
• Correct answer
  B

  $\left(\mathrm{a}\right),\mathrm{}\left(\mathrm{c}\right)$ and $\left(\mathrm{d}\right)$ only
• C

  $\left(\mathrm{b}\right)$ and $\left(\mathrm{c}\right)$ only
• D

  $\left(\mathrm{a}\right)$ and $\left(\mathrm{d}\right)$ only

Hence, the correct answer is option: 'B'.