Statement I:  ${\mathrm{BF}}_3$ is weaker Lewis acid than ${\mathrm{BCl}}_3$.
Statement II:  The planar ${\mathrm{BF}}_3$ molecule is stabilised to a greater extent than ${\mathrm{BCl}}_3\text{ by B }-\mathrm{X} \mathrm{back}\text{bonding. }$

Statement I is correct and statement II is incorrect.

Statement I is incorrect and statement II is correct.

Both statements I and II are incorrect.

Both statements I and II are correct.