Nitrogenous wastes are formed in the body because of the digestion of

Concept: The product of nitrogenous wastes occurs in the liver after the immersion of composites containing Nitrogen in the intestine. 

• The waste is excreted via order with urine and other protein products also. The introductory biomolecules present in our food are carbohydrates, proteins and lipids. 
• Nitrogen is also present in all of these. Amino acids contain nitrogen in the amino group and amino acids are the structure blocks of proteins. 
• Proteins are responsible for both nitrogenous as well as non- nitrogenous waste. 
• In humans, urea is a nitrogenous waste which is formed in the urea cycle.

Hence, option A is the correct answer.