The correct option is C Fluorine
Skeletal fluorosis or osteoporosis is a bone disease caused by excessive accumulation of fluoride in the bones. In advanced cases, skeletal fluorosis causes pain and damage to bones and joints. Due to a high fluorine concentration in the body, the bone is hardened and thus less elastic, resulting in an increased frequency of fractures. Other symptoms include thickening of the bone structure and accumulation of bone tissue, which both contribute to impaired joint mobility. Ligaments and cartilage can become ossified. As a result, bone flexibility decreases making the bone more amenable to fractures.