Which of the following best describes why hot air balloons rise? The molecular weight of the gases in the air increases when heated. Hot air is more dense than cold air creating a force or upward lift. The number of molecules in air increase exponentially when air is heated. Hot air is less dense than cold air , creating a force or upward lift.

The correct answer is: Hot air is less dense than cold air, creating a force or upward lift.<br /><br />When the air inside a hot air balloon is heated, it becomes less dense compared to the cooler air outside the balloon. This difference in density causes the balloon to rise due to buoyancy, as the denser, cooler air pushes the lighter, warmer air upwards.