[Ann1234]

hello, I am trying to understand this question but I am not getting an answer:

It says that "B electron configuration in BF4- is 1s2 2s1. Explain why"

I know the hybridization is sp3 in BF4^- and that B ground state is: 1s2 2s2 2p1

I have no clue why B configuration is 1s2 2s1 in BF4^-1.

Can someone give me a clue on how to explain this?

thanks