(1) One of the functions of blood is transport oxygen, carbon dioxide, enzymes, hormones etc. from one part of body to another so this statement is incorrect.
(2)Statement (b) is incorrect, because Human heart has four chambers-2 Atria and 2 ventricles.
(3) Both oxygen-rich and oxygen-deficient blood does not get mixed in the human heart as it has four chambers. The left side chamber-left atrium and left ventricle carry only oxygenated blood. Whereas right Atrium and right ventricle have only the deoxygenated blood and they do not get mixed in the process of circulation. Therefore, this statement is incorrect.
(4) Valves prevent backward flow of blood as they are located at each end of two ventricles and act as one way inlet.