Is Romeo and Juliet a tragedy? Support your answer.

This play is indeed a tragedy. Most broadly speaking, literature can be split into two broad groups: comedy or tragedy. A comedy, in this sense of the word, doesn't have to be funny or make you laugh. It only has to have a happy ending in the sense that things work out for the main characters, usually to keep them alive. Were Romeo to have gotten word at the last minute that Juliet was not really dead and had simply waited for her awakening, the play would have been a comedy, even with no laughs (though Shakespeare weaves in jokes earlier in the play). But, alas, everything goes wrong and both of the star-crossed lovers kill themselves. Even more typically tragically, they are fated to die and die due to a series of mistakes that could have been prevented. In a typically tragic way, their own  flaws contributed to their deaths: both acted on impulse, without fully thinking through what they were doing.