A mixture of benzene and aniline can be separated by

 A mixture of Benzene and aniline is shaken with dilute HCl in separating funnel Two layers separated. Aniline is a weak base with dil. HCl it gives black ppt. while benzene does not react with dil. HCl. Thus these can be separated by HCl. ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{N}{\mathrm{H}}_2\stackrel{\mathrm{dil}.\mathrm{HCl}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2.\mathrm{HCl}\downarrow$ 

Therefore correct option (C) $HCl$.