Lewis acidity of boron halides follow the order ( $\approx$ meaning approximately equal to)

• A

  $\mathrm{BF}_3 \approx \mathrm{BBr}_3 \approx \mathrm{BCl}_3$
• Correct answer
  B

  $\mathrm{BF}_3 \lt \mathrm{BCl}_3 \lt \mathrm{BBr}_3$
• C

  $\mathrm{BCl}_3 \approx \mathrm{BBr}_3 \lt \mathrm{BF}_3$
• D

  $\mathrm{BBr}_3 \lt \mathrm{BCl}_3 \lt \mathrm{BF}_3$

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