CBSE Class 10 Answered

Ethanol when reacted with hot conc. sulphuric acid at 443 K, forms ethene .

Onon adding potassium permanganate  to ethanol , the colour of the solution disappears because potassium permanganate os being consumed in the reaction to convert ethanol to ethanoic acid.

When excess of potassium permanganate is added, till ethanol is being converted to ethanoic acid, it remains as colourless. But when complete ethanol is converted, the potassium permangatanate is not being consumed and hence the left over potassium permanganate gives pink colour to the solution.