Explanation:

Human beings are ureotelic animals. They excrete mainly urea eliminated via the urine. Urea is a product of the degradation of amino acids.

• In this process, amino acids lose their amine group which is then transformed into ammonia.

• In the liver, ammonia reacts with carbon dioxide to form urea and water by a process known as ureogenesis.

• So, Urea is the main nitrogenous waste in human beings as they are ureotelic animals.

Hence option 2nd is correct.