Proteins consist of amino acids that are organic compounds composed of carbon (I), hydrogen (II), oxygen (III), and nitrogen (IV) atoms.

Option 1 includes only hydrogen (II) and oxygen (III) which are part of water molecules more than proteins.

Option 2 excludes oxygen (III), which is incorrect because oxygen forms part of the carboxyl group, linked to each amino acid that make up proteins.

Option 3, although it includes the carbon (I), oxygen (III) and nitrogen (IV), it omits hydrogen (II) which forms part of every amino acid in proteins.

Option 4 encompasses all four elements- carbon, hydrogen, oxygen, and nitrogen, which are all the basic building blocks of proteins. Hence, option 4 is the correct answer.