In the presence of $H_2SO_4$,ether is obtained from ethyl alcohol at which of the following temperatures (in $K$)?

$PCC$ is

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:

$CH \equiv CH$ $\xrightarrow{Hg^{2+}/H_2SO_4} B$ $\xrightarrow{CH_3MgX/H_2O} C$ $\xrightarrow{[O]} D$. What is the final product $D$?

The iodoform reaction is given by all of the following,except:

How many isomers of ${C_5}{H_{11}}OH$ are primary alcohols?