Ans. is 'c' i.e., Alkaptonuria * Individual presenting in 4th decade with joint pain and stiffness and urine darkening on standing and pigment deposition in joints, is suggestive of alkaptonuria.Ochronosis (Alkaptonuria):* Alkaptonuria is a rare, heritable disorder characterized by the appearance of homogentisic acid in the urine , darkpigmentation of the connective tissues (ochronosis ) and calcification of hyaline and fibrocartilage.* Inborn error is an absence of homogentisic acid oxidase in the liver and kidney. Those affected usually remainasymptomatic until the 3rd & 4th decade when they present with pain and stiffness of the spine & (later) larger joints.* Dark pigmentation of ear cartilage & sclera and staining of clothes by homogentisic acid in sweat. Urine turnsdark brown when it is alkalinized or if it is left to stand for some hours.* X- ray reveal narrowing & calcification of intervertebral discs. Peripheral joints show chondrocalcinosis &severe osteoarthritis.