The most stable Lewis acid-base adduct among the following is

• A

  $\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{BCl}_{3}$
• B

  $\mathrm{H}_{2} \mathrm{~S} \rightarrow \mathrm{BCl}_{3}$
• Correct answer
  C

  $\mathrm{H}_{3} \mathrm{~N} \rightarrow \mathrm{BCl}_{3}$
• D

  $\mathrm{H}_{3} \mathrm{P} \rightarrow \mathrm{BCl}_{3}$

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