What property stays the same during physical and chemical changes?

Mass doesn't change in physical or chemical change.
Physical change are changes that affect the form of a substance. Example is the change in the state of water from solid to liquid and to ice.

Chemical change is a type of change that occurs when a substance is changed from one form to another form that cannot be reversed. Chemical composition changes in chemical change.

Density and shape change in physical change, shape and arrangement of particles change in chemical change.
Remember the law of conversation of mass, that states that mass is neither created nor destroyed in physical or chemical change.