concentrated hydrochloric acid
Add concentrated hydrochloric acid dropwise onto a small quantity of potassium permanganate crystals (in a flask). Collect the chlorine gas by upward displacement of air in a hood. Use proper safety precautions. Concentrated hydrochloric acid is extremely caustic. Chlorine gas is toxic.
6HCl + 2KMnO4 + 2H+ --> 3Cl2 + 2MnO2 + 4H2O + 2K+