Answer:
it comes from your knowledge and the information you have to get the reason why that is the answer so you are putting together things that you already know what the new information you have
On your list you can easily identify by knowing which is not a chemical change.
A physical change is a change not involving the material composition of the water. e.g. (melting, solidifying, evaporation). As long as the change does not change the molecular composition of the water which is H20 it is physical change.
i think the answer is D 10.0
I believe the balloon would shrink from lack of oxygen.<span />
The answer would be . Since we are looking for the spring constant you would need to use the formula

. Then you'd substitute, for PEs and x.

Then solve. k=500n/m