If someone's diet is deficient in iodine, his thyroid gland may enlarge. This disease is known as goitre. Kelps are so rich in iodine, that people who consume kelps don't suffer from goitre at all. Oh, I see. Rest of the iodine is used for some other essential purposes.
Some commercial preparations containing iodine are povidone-iodine and tincture of iodine.
These are basically used as antiseptics and disinfectants. Ramlal probably kept the tincture of iodine in his general medical chest, as most of us do. Povidone-iodine is primarily used as a vaginal disinfectant. Tincture of iodine is usually applied on cuts and abrasions, to prevent them from getting infected. Then there is the strong iodine tincture, which was found in Ramlal's house.