Question

explain how air expand on heating

Answer 1

When air is heated, its molecules gain kinetic energy. Due to which they move away from each other. Therefore air expands on heating

Answer 2

hot air molecules,on average, have more space between them than cool air molecules. therefore when you heat air it expands to allow more space for he molecules. if you then cool the air , it contracts because cool air molecules need less space than hot air molecules.