Question

Are these cations, how do i know?
BF3, BH3, AlCl3, FeCl3

how do i recognize a cation?

Answer 1

Cations have a positive charge as in K^+, Na^+, Ca^+2, etc.
Anions have a negative charge as in SO4^-2, Cl^-, Br^-, etc.
What you have listed are neutral charge which means they are molecules.

Answer 2

Ok, thank you.