Free speech also known as freedom of speech is the right of a person to express opinions and ideas without interference.It should be based on three  factors:  knowledge, action and experience.

Example : Evaluation of online exam is not good. 

Hate speech is any form of expression through which speakers intend to  humiliate against a group or a class of persons on the basis of race, religion, gender identity, disability, or national origin.

Example : The same example in free speech is a hate speech for the exam committee.    

Offensive speech can be defined as speech that causes someone to feel resentful, to feel hurt, angry,  insulting, causes anger or annoyance. Which can create an argument, debate.

Example : The same example in free speech is also an offensive speech because there can be a debate between students.