When chlorine gas is passed through a solution of potassium bromide, the solution changes color from colorless to orange-brown.

Here's why:

* Chlorine is a more reactive halogen than bromine. This means chlorine can displace bromine from its compound.

* The reaction:

Cl₂ (g) + 2KBr (aq) → 2KCl (aq) + Br₂ (aq)

* The products:

* Potassium chloride (KCl) is colorless in solution.

* Bromine (Br₂) is a reddish-brown liquid that dissolves in water to give an orange-brown solution.

Therefore, the color change observed is due to the formation of bromine in the solution.