Which of the following substances gives a yellow precipitate with $I_2$ and alkali?

Among the following compounds,which one can be dehydrated very easily?

Which of the following is a secondary benzylic alcohol?

Which one of the following is a secondary alcohol?

$CH_3 CH_2 OH$ $\xrightarrow{Cl_2} CH_3 CHO$ $\xrightarrow{3 Cl_2} Cl_3 CCHO$. In the above reactions,the role of $Cl_2$ in step-$1$ and step-$2$ respectively is:

$(CH_3)_2CHOH$ $\xrightarrow{PCC} X$ $\xrightarrow[(ii) H_2O]{(i) CH_3MgBr} Y$. What is $Y$?