Carbon and Hydrogen are pure substances or elements. All the atoms of carbon have same number of protons. It cannot be broken into new elements.
Contrary to elements, there are compounds which are formed by the chemical bonds between two or more elements like in water. In water, Hydrogen and oxygen elements combine. All the atoms of water do not have the same number of protons. Then, there are mixtures where elements are not chemically bound. For example, air.
