Statement (a) is correct: During denaturation of proteins, the unfolding of the protein chain occurs, leading to the loss of its secondary and tertiary structures, thereby losing its biological activity. Statement (b) is correct: In the case of DNA, denaturation (due to heat or change in pH) breaks the hydrogen bonds between the base pairs, causing the double-stranded DNA to separate into two single strands. Statement (c) is incorrect: The primary structure of a protein (the linear sequence of amino acids held together by strong covalent peptide bonds) remains completely intact and unaffected during denaturation. Hence, only statements (a) and (b) are correct.