Complex sentence: Under standard conditions, iodine is a bluish-black solid with a metallic lustre, appearing to sublimate into a noxious violet-pink gas, the colour due to absorption of visible light by electronic transitions between the highest occupied and lowest unoccupied molecular orbitals.
Split into simpler sentences: Under standard conditions, iodine is a bluish-black solid with a metallic lustre, appearing to sublimate into a noxious violet-pink gas. The colour is due to absorption of visible light by electronic transitions between the highest occupied and lowest unoccupied molecular orbitals.