The teacher is teaching in a class of students. This can be the best example of

A teacher teaching a class of students is best described as group communication.

Here one speaker addresses a bounded, gathered set of learners who can interact, the mark of a group setting.

Face to face communication usually names a one-to-one personal exchange, narrower than a whole class.

Mass communication reaches a large, scattered and anonymous audience through media, unlike a present classroom.

Inter-cultural communication turns on exchange across differing cultures, which is not the defining feature here.

The bounded, present, interacting audience makes this a group situation.