2.12 explain, in terms of dissociation, why hydrogen chloride is acidic in water but not in methylbenzene

If HCL is dissolved in water, it dissociates (splits up) into H+ and Cl- ions. This solution (hydrochloric acid) is acidic because it contains H+ ions.

However, if HCL is dissolved in methylbenzene, it doesn't dissociate into H+ and CL- ions, therefore no H+ ions are present so the solution is not acidic.