- A Bronsted base needs a lone pair because the $H^+$ doesn't have any, and, in the reaction, one bond needs to be formed. - Therefore, the base needs a pair of electrons, so it can make a bond with the $H^+$.
Work Step by Step
- When a bond is being made, it is necessary to have a pair of electrons (Doesn't matter where they come from). - $H^+$ doesn't have electrons. - So, the electrons should came from the base.