Assertion :Liver is more important excretory organ than kidney. Reason: Urea is synthesized by ornithine cycle in liver.

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

• The Excretory system is responsible for the elimination of wastes produced by homeostasis.
• There are several parts of the body that are involved in this process, such as sweat glands, the liver, the lungs and the kidney system.
• In humans and mammals, almost 80% of the nitrogen excreted is in the form of urea, which is produced through a series of reactions occurring in the cytosol and mitochondrial matrix of liver cells.
• The urea cycle or ornithine cycle converts excess ammonia into urea in the mitochondria of liver cells. Hence, the Liver is more important excretory organ than kidney as Urea is synthesized by ornithine cycle in the liver.

So, the correct answer is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion'.