Explain why physical changes can easily be reversed but chemical changes cannot

Physical changes can easily be reversed but chemical changes cannot because in physical change only state is changed while in chemical change, new substances are formed. For example, when water in liquid form is condensed, it changes into solid form (ice). It is a physical change because water in liquid and solid have the same chemical formula only arrangement of molecules are different. Burning of wood is a chemical change because new substances i. e. carbondioxide and heat is produced.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.