The alcohol which does not give a stable compound on dehydration is

What is obtained when ethyl alcohol is heated with red phosphorus and $HI$?

Which of the following statements about glycerol is incorrect?

Glycerol on treatment with oxalic acid at $110 \ ^oC$ forms

What are $X$ and $Y$ in the following reactions?

$A$ hydroxy compound $(X)$ with molar mass $122 \ g \ mol^{-1}$ is acetylated with acetic anhydride,using a large excess of the reagent ensuring complete acetylation of all hydroxyl groups. The product obtained has a molar mass of $290 \ g \ mol^{-1}$. The number of hydroxyl groups present in compound $(X)$ is :