Which is used as an antifreeze?

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

Consider the following reaction sequence:
$CH_3CHO$ $\xrightarrow[(ii) H_3O^+]{(i) CH_3MgBr} A$ $\xrightarrow[\Delta]{Conc. H_2SO_4} B$ $\xrightarrow[(ii) H_2O, OH^-]{(i) B_2H_6} C$
$A$ and $C$ are:

Ethyl alcohol gives ethyl chloride with the help of ..........

Arrange the following alcohols in the decreasing order of their rate of dehydration via the $S_{N}1$ mechanism:

Dehydrogenation of $CH_3-CH(OH)-CH_3$ gives