The correct answer is option 2, Iodine solution. Iodine solution is commonly used to test for the presence of starch in leaves. When iodine solution is added to a leaf, it reacts with any starch present in the leaf and forms a blue-black color. This is due to the formation of a compound between the iodine and the starch molecules, which results in this distinct color change.
Option 1, Fehling`s solution, is used to test for the presence of reducing sugars, not starch. Option 3, Million`s reagent, is used to test for the presence of proteins. Option 4, Benedict`s solution, is also used to test for the presence of reducing sugars, not starch.
Therefore, option 2 is the correct answer as iodine solution is specifically used to test for the presence of starch in leaves.