The correct option is A Mob
A mob is a large, angry crowd, especially one that could easily become violent For example, "The angry mob outside the jail was/were ready to riot". Hence, Option C is correct. Among the rest of the options, crowd means a large number of people gathered together in a disorganized or unruly way, gathering means an assembly or meeting, especially one held for a specific purpose, congregation means a group of people assembled for religious worship. These do not express this meaning, hence incorrect.