Use of hot air ballons in sports and meteorological observations in an application of

Use of hot air balloon in sports and metorological observation is an application of

Assertion : The use of hot air balloons in sports and for meteorological observations is an application of Charle's law Reason : Hot air is less and hence gases expand on heating

Use of hot air ballon in meteorological observatory is an application of :

How do hot air balloons float?

Why do hot air balloons float?