Biological molecules and their elemental composition

Steps:

• Recall that biological molecules have distinct chemical formulas based on their structure.
• Identify elements in DNA: it includes nucleotides with sugar (C, H, O), phosphate (P, O), and nitrogenous bases (C, H, O, N).
• Check other options: carbohydrates like cellulose and starch contain only C, H, O; lipids typically contain C, H, O (though some variants add P or N).
• Confirm DNA uniquely matches all required elements (C, H, N, P) among the choices.

Why A is correct:

• DNA's structure includes deoxyribose (C, H, O), phosphate groups (P, O, H), and bases like adenine (C, H, N), providing C, H, N, P.

Why the others are wrong:

• B. Cellulose is a polysaccharide made of glucose units, containing only C, H, O.
• C. Lipid generally refers to fats and oils with C, H, O; lacks N and P in basic forms.
• D. Starch is a carbohydrate polymer of glucose, composed solely of C, H, O.

Final answer: A