Smoke filling up a room is indeed an example of diffusion. Diffusion occurs when two or more sets of molecules intermingle and spread out. In this case, it would be the smoke molecules interacting and spreading out among the air molecules.
Answer: when a writer points to a problem caused by social customs without explicitly challenging those customs.
A social commentary is the use of rhetorical devices in order to comment on the problems of society. This is usually a critique, and it is intended to promote change or to appeal to people's sense of justice. However, when this commentary is done subconsciously, the writer points towards the problem but does not explicitly challenge the customs.
