For the reaction, identify the lewis acid and the lewis base. alf3 + ch3f → ch3+ + [alf4]-

            AlF₃ is Lewis Acid

            CH₃F is Lewis Base

Explanation:
                     According to Lewis concept ,"those compounds which donate pair of electrons are called as Lewis Base and those accepting pair of electrons are called as Lewis Acid.

In Given Reaction,
                               AlF₃ + CH₃F → CH₃⁺ + [AlF₄]⁻

AlF₃ is acting as acid because the octet of Al is not complete, hence it has tendency to accept electrons.

CH₃F is acting as a base because the F atom containing three lone pair of electrons can donate it to Al metal resulting in the formation of electrophile i.e. CH₃⁺.