What amongst the following is responsible for formation of stone in human kindey?

Calcium oxalate is the answer. It makes up roughly 70 to 80 per cent of kidney stones, and most of the rest are calcium phosphate or uric acid. Urine becomes supersaturated with calcium and oxalate, crystals nucleate and grow, and low urine volume makes this worse. Oxalate comes partly from the diet (spinach, tea, nuts, rhubarb) and partly from the body's own metabolism, which is why hyperoxaluria is a recognised cause of stones.

Why the others are wrong:

• Calcium acetate is a phosphate binder given to patients with chronic kidney disease. It is taken with meals to bind dietary phosphate in the gut, so it is a treatment, not a cause.
• Sodium acetate is used as an electrolyte source and buffer in IV fluids. It has no role in stone formation.
• Sodium benzoate is a food preservative (E211). It is also used in urea cycle disorders to help remove nitrogen, and it does not form urinary stones.

Core concept: urolithiasis and urinary supersaturation. It links to Mains questions on lifestyle diseases, diet and hydration.

Trap: calcium acetate contains calcium, so students pick it by association. The stone-forming part is the oxalate anion, and the acetate salt is actually given to protect kidney patients.