Three quarters of a PET bottle are filled with a soft drink. When you open the bottle, you can smell what is inside. Now you squeeze the bottle so that the liquid rises to the opening and all the gas phase is pushed out of the bottle. When you let the bottle go, it returns to its original shape and fresh air without any smell is sucked in. Now you close the bottle and let it sit for a few hours.
When you open the bottle again after a few hours:
It will smell almost the same as it did in the beginning of this experiment because scent molecules have moved from the liquid to the gas phase again.
It does not smell any more because the gas phase that contained the scent was replaced by fresh air.
When you open the bottle a day later:
There is still no smell.
The scent is stronger than at the day before because scent molecules are constantly moving from the liquid to the gas phase and accumulate there.
Neither answer a) nor answer b) is correct.
When you repeatedly squeeze out the air from the headspace of the bottle:
The strength of the smell will decline because you are continuously removing scent molecules from the system. Also the liquid will lose its taste.
The scent in the headspace will stay the same because the displaced scent molecules will always be replaced by those that move from the liquid to the gas phase. However, the liquid will lose its taste.
The scent in the gas phase had nothing to do with the liquid. Once the gas phase is replaced, any new gas phase will never smell again like it did in the beginning. The taste of the liquid will remain unchanged.