The last description makes the most sense, as to how the wording "mob" and "populace" imply them as behaving as group. Called social group psychology, many people "join the crowd" when it comes to supporting or opposing certain events, causes, or acts.
The sentence that does not contain any errors in comma usage is option C. Mick introduced me to his dog, a golden retriever. The word "dog" and the phrase "a golden retriever" is separated by a comma because the phrase "a golden retriever" is an example of an appositive phrase. An appositive is a phrase that is used to rename or describe the noun it precedes. In this case, the phrase "a golden retriever" renames the word "dog". Appositive phrases which are additional information should always be set off by a comma or a pair of commas.
Mohamed Abdullahi Mohamed