The opposite of responsible is:
mortal
loose
delighted
joint

I think the opposite is loose

Explanation:

Because responsible is being able to be trusted to do a task right? So loose would be the opposite since if you're loose(crazy,out of control,ect) you wouldn't be trusted as being responsible

dramatic irony occurs when the reader/audience knows more about a character's situation than the character does. the one main effect is that it gives the reader a sense of superiority, or detached superiority. the reader not only seemingly discovers what is revealed, but feels superior for doing so.