Boron trifluoride on reaction with lithium aluminium hydride in ether gives $\mathrm{LiF}, \mathrm{AlF}_3$ and X. X on reaction with $\mathrm{NH}_3$ gives Y. Y on further heating gives a compound Z. The number of $\sigma$-bonds and $\pi$-bonds in Z are $x$ and $y$ respectively. $(x+y)$ is equal to

• Correct answer
  A

  $15$
• B

  $12$
• C

  $14$
• D

  $18$

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