Do amphibians breath air and water?

yes they do.

the oxygen in the air is already broken down enough so that the amphibians can breathe it. the process is slightly more complicated in the water. every molecule of water is formed of two atoms of hydrogen and an atom of oxygen. the amphibian swallows the water, and its body decomposes the molecule of water into its components (the process is called hydrolysis). then, the amphibian breathes the oxygen normally. however there are still two atoms of hydrogen left. these two atoms are bound in a reaction of nuclear fusion and form an atom of Helium. the amphibian releases the helium from its mouth, hence the weird squeaky sounds some of them make (frogs)