What is the colour of KMnO₄?

Purple 

The correct answer is option 3. Purple.

The purple color of potassium permanganate (KMnO₄) is attributed to the presence of the permanganate ion (\(MnO_4^-\)). The permanganate ion has a deep purple or dark violet color, and this color arises due to the absorption of light in the visible spectrum.

The permanganate ion absorbs light in the red and green regions of the spectrum, allowing the blue and violet light to be transmitted or reflected. As a result, the overall appearance of the compound is purple to the human eye.

The intense purple color of KMnO₄ makes it easily recognizable and is often used in laboratory experiments and titrations as an indicator or as an oxidizing agent.