Among BF₃, NF₃, OH⁻ and ALCl₃ both NF₃ and OH⁻ acts as a lewis base.
Explaination:
According to lewis theory of acid and base, base is a specie which has either lone pair of electrons or is negatively charged. So, in the given compounds Nitrogen trifluoride contain lone pair of electron on nitrogen and Hydroxide contains a negative charge on oxygen. And botha are capable to donate these electrons to a lewis acid (electrophiles).
