HCl, HClO, all acids can be absorbed by alkali. Therefore, alkali liquor is enough for tail gas treatment. NAOH is more expensive than Ca(OH)2, so it depends on the economic conditions of the laboratory.

Preparation of Cl2: MnO2+4HCl (concentrated) =MnCl2+Cl2+2H2O, so CHl will escape with the gas flow, and HCl can also be absorbed by tail gas treatment.