Today I will explain what a valence electron is and how many valence electrons each of the atoms your asking about have. :)
→ A valence electron is an electron in the outer shell of an atom that is able to participate in bonding. While iodine has 53 electrons, all but seven are in the inner shells of the iodine atom.
→ Sulfur has sixteen electrons in total, two in the inner shell, eight in the middle, and six in the outer. This means that sulfur has six valence electrons.
↑ ↑ ↑ Hope this helps! :D