The correct answer option is 4, Bone. Vitamin D is essential for maintaining strong and healthy bones. It plays a crucial role in absorbing calcium and phosphorus from the diet, which are necessary for bone health. Vitamin D deficiency can lead to several bone-related problems, such as thinning of the bones (osteoporosis) and softening of the bones (osteomalacia). Osteoporosis increases the risk of fractures, while osteomalacia can cause bone pain, muscle weakness, and difficulty walking. While eyes, skin, and hair can be affected by various factors, they are not directly associated with Vitamin D deficiency. It`s important to ensure an adequate intake of Vitamin D through sunlight exposure and/or dietary sources to maintain optimal bone health.