A mixture of benzoic acid, aniline and nitrobenzene dissolved in ether is shaken first with aqueous $\mathrm{NaHCO}{}_3$ and then, after separation, with dilute $\mathrm{HCl}$. The substance remaining in the ether layer at the end is:

Benzoic acid reacts with bicarbonate to give water-soluble sodium benzoate and leaves the ether layer. Aniline is basic and reacts with dilute $\mathrm{HCl}$ to give water-soluble anilinium chloride, which also leaves the ether. Nitrobenzene is neutral and not basic enough to be protonated, so it stays in the ether.