User registration and chat communication between users -- 3

I need simple website single page for user registration & one user call to chat button to start chatting like (Facebook chat). description User (A)fill the form for question and other user(B,C,D...more) apply for answer then both can start chatting that's all. But user only can start chat who has posted question then other user can start chat. Note:- When user (A) post question he ll select category question type i ll create categories from admin panel.