Formation of diethyl ether from ethanol is based on a

Propene is the product obtained by the dehydrogenation of

The number of primary $(1^{\circ})$,secondary $(2^{\circ})$ and tertiary $(3^{\circ})$ alcohols possible for the formula $C_5H_{12}O$ respectively are

An organic compound $X$ on treatment with $PCC$ in dichloromethane gives the compound $Y$. Compound $Y$ reacts with $I_{2}$ and alkali to form a yellow precipitate of triiodomethane. The compound $X$ is

$A$ on heating isomerizes to $B$. What is the structure of $B$?

Which of the following substances gives a yellow precipitate with $I_2$ and alkali?