Question:
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b 1,2,3 Triiodopropane eliminates 2 HI

When excess of HI is added in vicinal diols ,this results in elimination of water and all OH groups are replaced by I^-.But compound 1,2,3-triiodopropane is very unstable and it undergoes elimination of I₂ to give 3-iodoprop-1-ene.This compound has a carbon -carbon double bond so it can undergo further addition of HI by Markownikov's rule to give 1,2-diiodopropane. This is followed by elimination of I₂ to give Propene .However there is excess of HI so further addition of HI will take place to give 2-iodopropane..
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Quote from: chenbeier on September 29, 2022, 09:44:34 PM
b 1,2,3 Triiodopropane eliminates 2 HI

Explain your answer?
Check it is excess of HI 

The question is, how HI is added as a gas or as Hydrogeniodide acid solution. I agree to your mechanism in solution. But in my opinion the Triiodopropane is aprotic and not solouble in glycerol water solution and will evaporate. The decomposition normaly goes easier to eliminates HI and not I2. So from the given solutions only the allyliodide would be left. Of course all could be equilibrium  reactions.

Quote from: chenbeier on September 30, 2022, 05:28:08 AM
The question is, how HI is added as a gas or as Hydrogeniodide acid solution. I agree to your mechanism in solution. But in my opinion the Triiodopropane is aprotic and not solouble in glycerol water solution and will evaporate. The decomposition normaly goes easier to eliminates HI and not I2. So from the given solutions only the allyliodide would be left. Of course all could be equilibrium  reactions.

First they have not written gas any where
Second OH of glycerol  is protic and oxygen lone of OH can take H+ from HI.
Second in water is eliminated so it is present in solution.

QuoteFirst they have not written gas any where

There is also not mentioned in solution. It is said only excess of HI.
But in the reaction glycerol an HI water is obtained that the aqueous mechanism is probably preferred.

Quote from: chenbeier on September 30, 2022, 06:01:46 AM
There is also not mentioned in solution. It is said only excess of HI.
But in the reaction glycerol an HI water is obtained that the aqueous mechanism is probably preferred.

So finally my answer is correct.