is it possable to make a chat room on scratch?

No. This is against the Scratch guidelines. Sorry. Scratch on!

This should go in Questions about Scratch, just FYI.

Anyways, yes, it is allowed, but ONLY if users are only allowed to pick from a certain set of phrases or words - so like you could have a whitelist of words, such as:

hi
bye
hello
goodbye
how
are
you
doing
…

And your program would check to see if the sentence typed in only contained those words, and if so, output it, otherwise, it would do nothing.