Correct Answer: A
Explanation:
Alkenes react with potassium manganate (VII) solution in the cold. The colour change depends on whether the potassium manganate (VII) is used under acidic or alkaline conditions.
If the potassium manganate (VII) solution is acidified with dilute sulphuric acid, the purple solution becomes colourless.
If the potassium manganate (VII) solution is made slightly alkaline (often by adding sodium carbonate solution), the purple solution first becomes dark green and then produces a dark brown precipitate.
Manganate (VII) ions are a strong oxidising agent, and in the first instance oxidise ethene to ethane-1,2-diol (old name: ethylene glycol).
Looking at the equation purely from the point of view of the organic reaction: