When you talk about communication through mass media, it refers to any kind of communicating medium or channel that directly reaches to a "massive audience".
Now lets look at the examples and see if the message is communicated to "massive audience" or just a small crowd.
1. An advertisement in a magazine (YES it is an example of communication through mass media because magazine reaches to countless people)
2. A blog about how to grow flowers (YES it is an example of communication through mass media because the blog would be accessible to people around the globe and a huge number of people can follow it)
3. A group of men discussing the weather (Its NOT an example of communication through mass media because it clearly involves a 'group' of men which surely does not come under massive audience)
4. A political poster promoting a political party (YES it is an example of communication through mass media because the poster would probably be placed at a place where numerous people from all walks of life would pass by and will get a chance to look at)
5. A teacher discussing literature in a classroom (Its NOT an example of communication through mass media because a teacher would be reaching many students in a class but the students would still not be a massive audience)
