Which of the following is a tertiary alcohol?

Optically active $2-$octanol rapidly loses its optical activity when exposed to

$A$ toxic compound $A$ when reacted with $NaCN$ in aqueous acidic medium yields an edible cooking component and food preservative $B$. $B$ is converted to $C$ by diborane and can be used as an additive to petrol to reduce emission. $C$ upon reaction with oleum at $140^{\circ} C$ yields an inhalable anesthetic $D$. Identify $A, B, C$ and $D$,respectively.

Which one of the following compounds will provide a tertiary alcohol on reaction with excess of $CH_3MgBr$ followed by hydrolysis?

$CH_3-CH(OAc)-Et$ ($d=$ dextro rotatory) $\xrightarrow{HO^{-}}$ Product of the reaction is

In the following sequence of reactions,
$CH_3CH_2CH_2Br$ $\xrightarrow{KOH(alc.)}$ $(A)$ $\xrightarrow{HBr}$ $(B)$ $\xrightarrow{KOH(aq.)}$ $(C)$
The product $(C)$ is