The chemical element with the symbol 'I' is iodine. Iodine is a vital trace element, crucial for the synthesis of thyroid hormones, which play a significant role in regulating metabolism, growth, and development in humans and animals. It is commonly found in seaweed, fish, dairy products, and iodized salt. Iodine deficiency can lead to health issues such as goiter and developmental disorders. Aside from its biological importance, iodine is also utilized in various applications such as disinfectants and in the manufacturing of pharmaceuticals. Its distinct blue-black color when reacting with starch makes it a useful indicator in analytical chemistry.