The gas in the piston is being heated, and the piston has moved upward. the observation will be summarized in a row of the incomplete table below. row : 1, 2, 3, 4 name: boyle's law, charles’s law, gay- lussac's law, combined gas law observation: volume increases when pressure decreases, ? , ? , ? variables: ? , ? ,temperature, pressure, ? what are the variables for this piston? 1. temperature only 2. temperature and volume 3. pressure and number of molecules 4. volume and number of molecules