The correct answer is option 2, Riboflavin. Riboflavin, also known as vitamin B2, is a water-soluble vitamin that is essential for the body`s growth and overall health. It plays a vital role in converting food into energy and is necessary for maintaining proper vision and healthy skin. Riboflavin also acts as an antioxidant, helping to protect the body`s cells from damage caused by free radicals. It can be found in various foods such as milk, eggs, green leafy vegetables, and whole grains.

Option 1, Keratin, is not a vitamin but a protein that is a major component of hair, skin, and nails. Option 3, Insulin, is a hormone produced by the pancreas that regulates blood sugar levels and is not a vitamin. Option 4, Adrenalin, is a hormone released by the adrenal glands in response to stress and is also not a vitamin.