Order of toxicity among ammonia, urea and uric acid (from lower to higher) is
a)	Uric acid < urea < ammonia	b)	Uric acid < ammonia< urea
c)	Urea < uric acid < ammonia	d)	Ammonia < urea < uric acid

(a)

(i) Ammonia ( ) It is the first metabolic waste of the protein metabolism. Ammonia is produced in the liver by the process of deamination. Ammonia is very toxic and requires large amount of water for its excretion

(ii) Urea White crystalline solid product produced in the liver from  and . It is comparatively less toxic. Normal level of urea is 18-38 mg/100 mL of the blood

(iii) Uric Acid It is least toxic and insoluble in water. It is produced in the liver by purine catabolism in birds, and reptiles. It can be excreted in solid or semisolid form. Excretion of uric acid in solid or semisolid form conserve water. Uric acid is commercially extracted from the bird dropping (guano)