What is the major defining property of
gasses?

Measuring which physical property is most likely to produce the most precise results when trying to identify a substance

Iknow the answer is a but i don't know why

Harvey kept a balloon with a volume of 348 milliliters at 25.0˚c inside a freezer for a night.  when he took it out, its new volume was 322 milliliters, but its pressure was the same.  if the final temperature of the balloon is the same as the freezer’s, what is the temperature of the freezer? the temperature of the freezer is  kelvins.