Study of kidneys is known as:

Option 1: Odontology -> Study of teeth and oral structures.

Option 2: Neurology -> Study of the nervous system and its disorders.

Option 3: Hematology -> Study of blood and blood-related diseases.

Option 4: Nephrology -> Study of kidneys and their functions.

Hence, Option 4: Nephrology -> The term is derived from the Greek word "nephros" meaning kidney. Nephrologists diagnose and treat kidney diseases, manage dialysis, and handle conditions like kidney stones and renal failure -> correct