Explanation: Fluorine occurs in nature as fluoride, in air, soil and water. Fluorisis is a common problem in several states of the country due to intake of high fluoride content water.

• Fluorides cause dental fluorisis, stiffness of joints (particularly spinal cord) causing humped back.
• Pain in bones and joint and outward bending of legs from the knees is called Knock-Knee syndrome.
• In cattle, fluoride intake causes staining, mottling and abrasion of teeth, lameness and decrease in milk production.

Source: Shankar IAS