One mole of glycerol is treated with an excess of HI to obtain isopropyl iodide. The number of moles of HI consumed by one mole of glycerol in this reaction is:
When glycerol is heated with 3 moles of HI, the allyl iodide formed first is reduced to propene. Propene in presence of excess of HI forms iso-propyl iodide.
From the reaction, it can be seen that five moles of HI are consumed by one mole of glycerol to finally form isopropyl iodide.
So correct answer is 5.