In the chemical reactions given above $A$ and $B$ respectively are :

• Correct answer
  A

  ${\mathrm{H}}_3{\mathrm{PO}}_2$ and ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}$
• B

  ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}$ and ${\mathrm{H}}_3{\mathrm{PO}}_2$
• C

  ${\mathrm{H}}_3{\mathrm{PO}}_2$ and ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}$
• D

  ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}$ and ${\mathrm{H}}_3{\mathrm{PO}}_2$

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