Achange occurs when a substance changes phase.
physical
chemical
nuclear

A physical change occurs when a substance changes phase.

For example, boiling pure water (H₂O) is physical change of substance (from liquid to gaseous state). In physical change, the bonds between oxygen and hydrogen can not be separated.

Sublimation of iodine (from solid to gas state) is also physical change.

Physical property can be observed and measured without any changes in molecular composition. The same substance is present before and after the change.

not clear