Nitrogen is NOT an essential constituent of

1. A

   Chlorophyll

   Option (a) claims that nitrogen is an essential constituent of chlorophyll. This is incorrect because chlorophyll molecules contain a central magnesium atom surrounded by a porphyrin ring made of carbon, hydrogen, oxygen, and nitrogen.

2. B

   RNA

   Option (b) claims that nitrogen is an essential constituent of RNA. This is incorrect because ribonucleic acid contains nitrogenous bases along with ribose sugar and phosphate groups.

3. C

   DNA

   Option (c) claims that nitrogen is an essential constituent of DNA. This is incorrect because deoxyribonucleic acid is built from nucleotides that include nitrogenous purine and pyrimidine bases.

4. D

   Carbohydrate

   Option (d) claims that nitrogen is not an essential constituent of carbohydrate. Official key is (d) because carbohydrates are organic compounds composed strictly of carbon, hydrogen, and oxygen, containing no nitrogen.

Summary. Official key is (d) as carbohydrates consist exclusively of carbon, hydrogen, and oxygen atoms. Chlorophyll contains a porphyrin ring structure where nitrogen is a vital coordinating element. Both RNA and DNA rely heavily on nitrogenous bases to store genetic information. Thus, carbohydrates stand apart from proteins, nucleic acids, and photosynthetic pigments by lacking nitrogen entirely.