Answer key says that A is the most basic site but I don’t understand the concept behind that.
To assess the basic site, I’d normally look at the molecule as is and assess the current stability of the atom in question. The least stable would be my strongest base.
Looking at this question both the atoms properties are the same (C with lone pair) so resonance is the next thing I would look at. Both of these rings have resonance which moves (delocalizes) the negative charge around. So I would think since the volume of resonance is greater in the bigger ring, A is more stable thus making B the stronger base.
What am I misunderstanding or what concept am I not considering?