Use of "it" and "that"
1. My boyfriend says he'll give up smoking but I don't believe it.
Can I use "that" instead of "it"?
2. I don't want to talk about that?
Can I use "I don't want to talk about it?"
Is "it" =that?
In what circumstances should we use "it" and "that" at the end of a sentence?
NOT A TEACHER!
I don't know the answer to your very last question, but I believe that you can use "it" and "that" on those two statements interchangably.
However, it does not ALWAYS mean that. Especially, if the statement is a part of a very long essay. The reader could get confused what "that" really refers to.