The high boiling point of ethanol $({78.2 \ ^\circ C})$ compared to dimethyl ether $({-23.6 \ ^\circ C})$,though both have the same molecular formula $C_2H_6O$,is due to

$PCl_5$ reacts with a compound containing

Consider the following alcohols:
$(I)$ $C_6H_5CH_2OH$
$(II)$ $O_2N-C_6H_4-CH_2OH$ (para-nitro)
$(III)$ $CH_3O-C_6H_4-CH_2OH$ (para-methoxy)
$(IV)$ $Br-C_6H_4-CH_2OH$ (para-bromo)
The order of decreasing reactivities of these alcohols towards nucleophilic substitution with $HBr$ is:

Propene is the product obtained by the dehydrogenation of

What is the major product of the following reaction?
$CH_3-CH(OH)-CH_2-CH_2-OH \xrightarrow[Pyridine, \text{cold}]{CrO_3} \text{Product}$

Which of the following compounds on oxidation gives ethyl methyl ketone?