Digesting a candy bar is a physical change or chemical change? why?

Aroom with dimensions 7.00m×8.00m×2.50m is to be filled with pure oxygen at 22.0∘c and 1.00 atm. the molar mass of oxygen is 32.0 g/mol. how many moles noxygen of oxygen are required to fill the room? what is the mass moxygen of this oxygen?

Which terms are used to identify pure substances

When did stem cell research become known ? who discovered stem cell? what experiments or studies have been conducted so far?