What is excretion? Name the excretory substances in animals.

(N/A) Excretion is the biological process by which an organism eliminates metabolic waste products from its body to maintain homeostasis.
Animals accumulate various metabolic wastes such as ammonia,urea,uric acid,carbon dioxide $(CO_{2})$,water,and ions like $Na^{+}$,$Cl^{-}$,$K^{+}$,phosphates,and sulphates.
These substances are collectively known as excretory substances,and the process of their removal is termed excretion.