Iodine solution is stored in coloured bottles to protect it from light. Here's why:

* Light sensitivity: Iodine is sensitive to light, particularly ultraviolet (UV) light.

* Decomposition: Exposure to light can cause iodine to decompose, breaking down into less active forms and reducing its effectiveness. This decomposition can also result in the formation of impurities.

* Coloured bottles block UV light: Brown or amber-coloured bottles effectively filter out UV rays, which prevents the iodine solution from being exposed to the damaging light.

By storing iodine solution in coloured bottles, you can ensure its stability, potency, and effectiveness over time.