Question

which element is found in both dna and protein?
sulfur
sodium
nitrogen
chlorine

Explanation:

DNA is a nucleic - acid composed of nucleotides, which contain nitrogen in their nitrogen - containing bases. Proteins are made up of amino acids, and amino acids have an amino group ($-NH_2$) which contains nitrogen. Sulfur is sometimes present in proteins (in amino acids like cysteine and methionine) but not in DNA. Sodium and chlorine are not major components of DNA or proteins.

Answer:

C. nitrogen