Well, you left out a huge bit of this question.
It's asking which compound out of (benzoic acid, toluene, aniline, and phenol) will end up in the aqueous (water) layer after adding the bicarbonate (NaHCO3).
So, we know NaHCO3 is basic and wants to steal a hydrogen. So who has the most acidic hydrogen? The carboxylic acid right (the benzoic acid), so he'll lose a hydrogen and ionize (become an ion) and float around with the Na+ ions, as sodium benzoate, a polar molecule, and as we know, like dissolves like, so it'll end up with our polar water layer.
I'm assuming you just didn't understand why it ends up in the aqueous layer (given that the answer section shows the benzoic acid losing a proton to the sodium bicarb). So, just remember, like dissolves like, polar molecules end up in the aqueous layer, while non-polars in the ether layer or non-polar layer. You might also review acidity of different compounds (stability), etc.
