Which of the following compounds gives a racemic mixture on nucleophilic substitution?
$(a)$ $CH_3-CH(Br)-C_2H_5$
$(b)$ $CH_3-C(Br)(CH_3)-C_2H_5$
$(c)$ $C_2H_5-CH(C_2H_5)-CH_2Br$

In which of the following reactions does an $SN^1$ reaction take place?

Alkyl iodides on keeping become dark in color due to ...........

Which of the following compounds has the highest boiling point?

In the following reactions,
$(i) CH_3-CH(CH_3)-CH(OH)-CH_3 \xrightarrow{H^{+}/\text{heat}} A \text{ [Major product]} + B \text{ [Minor product]}$
$(ii) A$ $\xrightarrow[\text{in absence of peroxide}]{HBr, \text{dark}} C \text{ [Major product]} + D \text{ [Minor product]}$
the major products $(A)$ and $(C)$ are respectively:

In the following reaction sequence,the correct structure$(s)$ of $X$ is (are)
$X$ $\xrightarrow[2) NaI, Me_2CO]{1) PBr_3, Et_2O}$ $\xrightarrow{3) NaN_3, HCONMe_2} \text{enantiomerically pure product}$