The correct answer is option 4, Vitamin D. Vitamin D is synthesized in our skin when it is exposed to sunlight. The process starts when the ultraviolet B (UVB) rays from the sun interact with a form of cholesterol in our skin called 7-dehydrocholesterol. This interaction leads to the production of previtamin D3, which is then converted into active Vitamin D3 in the liver and kidneys. Vitamin D plays a crucial role in maintaining bone health by aiding in the absorption of calcium and phosphorus from the intestines. It also has important functions in the immune system and has been linked to a lower risk of certain diseases, such as multiple sclerosis and certain types of cancer. However, it`s important to note that while sun exposure is a natural way to obtain Vitamin D, it`s also important to protect your skin from excessive sun exposure and wear sunscreen to prevent skin damage and reduce the risk of skin cancer.