Which amongst the following will be most readily dehydrated under acidic conditions?

Consider the following alcohols. The order of decreasing reactivities of these alcohols towards substitution with $HBr$ is:
$(I)$ $C_6H_5CH_2OH$
$(II)$ $p-NO_2-C_6H_4CH_2OH$
$(III)$ $p-CH_3O-C_6H_4CH_2OH$
$(IV)$ $p-Br-C_6H_4CH_2OH$

When ethyl alcohol $({C_2}{H_5}OH)$ reacts with thionyl chloride,in the presence of pyridine,the product obtained is

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

Which of the following compounds will form a hydrocarbon on reaction with a Grignard reagent?

Which one of the following is a secondary alcohol?