20. Carbohydrates are usually composed of sequences of carbon (C), hydrogen (H), and oxygen (O). How do proteins differ from carbohydrates?
A All proteins contain iron (Fe).
B. All proteins contain helium (He).
All proteins contain nitrogen (N).
D.
All proteins contain potassium (K).

Structurally, proteins are different from carbohydrates because all proteins contain nitrogen (option C).

Explanation:

The basis of the chemical composition of proteins is carbon, hydrogen, oxygen and nitrogen, so all proteins have nitrogen in their structure. Some proteins also possess phosphorus and sulfur atoms, among others.

Proteins are biomolecules formed by the union of multiple amino acids through carboxyl-amino bonds, called petidic bonds. Their content of nitrogen and other atoms in their structure is what makes them different from carbohydrates.

The other options are not possible because: