Hint: Our liver produces ammonia, which contains nitrogen- after its breakdown, proteins used by our body cells. The nitrogen combines with other elements, such as, carbon, hydrogen and oxygen, to form urea, which is a chemical waste product.
Urea, which is also known as carbamide. They are organic compounds.Urea plays an major role in the metabolism of nitrogen containing compounds by animals and is the most important nitrogen containing substance in the urine of mammals. physically they are colorless, odorless solid, highly soluble in water, and almost non-toxic .When they were dissolved in water they were neither acidic nor alkaline. The body utilizes it in many processes the majority especially nitrogen excretion. The liver produces urea by combining two ammonia molecules with a carbon dioxide molecule in the urea cycle. Urea is extensively used in fertilizers as a source of nitrogen and is a major raw material for the chemical industry.
The urea travels from our livers to our kidneys through our bloodstream. Healthy kidneys filter urea and remove other waste products from our blood. The filtered waste products leave our body through urine.
From the glomerular filtrate, the majority of the urea is excreted in urine but some quantity of urea is reabsorbed. For this reason, it is found in blood. The normal range of urea in 100 ml of human blood is about 17- 30 mg.
The presence of urea in blood and confirmation of its identity with that found in urine was demonstrated in 1822 but reliable methodology for determination of concentration of urea in blood had to wait until the early years of the 20th century.
Hence, the correct answer is option (C)
Note: If kidney problems are the main concern , the creatinine levels in our blood will likely also be measured when our blood is tested for urea nitrogen levels. Creatinine is another waste product that healthy kidneys filter out of our body through urine. High levels of creatinine in our blood may be a sign of kidney damage.