Hey, you're question doesn't make sense, can you make it clearer?
What I mean is what kind of balloon? Is it an air balloon or a simple balloon, Or to put it simply, what is the situation of the balloon for it to be pushed up?
Oh, I'm sorry, the one you've been chatting to was not me, it was someone else,
oh ok !!!
im so sorry !! :D
The answer that I know would be the balloon will get smaller, sorry for the late reply, my phone was out of battery, anyways I hope I helped ^_^
Is it grade 8 science? ballon is like example of our lungs,when our lungs move up ,we inhale, the space in our lungs become smaller and oxygen take place as we breathe in.

oh? sorry i answer incorrectly. carbon dioxide will take place as we breathe out. Try imagine it.