The atomic number of iodine is 53.
its elecronic configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5. it can be also written as [Kr] 4d105s25p5 using nobel gasses.the order of filling electrons in any enelment is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p. this depends on the energy.we know that electrons in an atom fill depending on their energy levels- 4s has more energy than 3d thats why it is written before 3d. so in iodine the electrons fills depend on the orbital's capacity. s' has capacity of 2,p has 6, d has 10. after filling one orbital it goes to other since there is no place to fill electrons beyond their capacity