Question

On heating water it evaporates then how ot will expand

Answer 1

Water expands because of anomalous expansion of water.
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Answer 2

water exhibits an unusual property called anomalous expansion. it makes water contract when heated from 0to4 degree Celsius and expand after that. While cooled it again expands on being cooled from 4to0 degree Celsius . when water turns into vapour state the kinetic energy of its molecules increases and so does the intermolecular space thereby expanding.
Hope it helps u