Which element is found in nucleic acids but not in proteins?

a. carbon
b. hydrogen
c. nitrogen
d. phosphorus

For the answer to the question above, it is phosphorous.
The nucleic acids also typically contain phosphorous, and nitrogen plays an important structural role in nucleic acids and proteins. The proteins, being made up a diverse set of amino acids, have, in addition to carbon, hydrogen, oxygen, and nitrogen, the elements sulfur and selenium except for phosphorous