Identify the compound $\mathrm{D}$ in the following series of reactions:

The compound, which is not formed when a mixture of $\mathrm{n}-\text{butyl bromide}$ and $\mathrm{ethyl} \mathrm{bromide}$ treated with $\mathrm{Na}$ metal in the presence of dry ether is _______.

A mixture of two organic chlorine compounds was treated with sodium metal in ether solution and isobutane was obtained as a product. The two chlorine compounds are ______.

The order of reactivity of methyl halides in the formation of Grignard reagent is _______.

Identify $\mathrm{X}$ and $\mathrm{Y}$ in the following sequence ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{Br }\stackrel{\text{X}}{\to }\text{product }\stackrel{\text{Y}}{\to }{\text{ C}}_{\text{3}}{\text{H}}_{\text{7}}{\text{NH}}_{\text{2}}$

What is the chemical composition of $\text{Nicol's prism}$?

The number of asymmetric carbon atom(s) in lactic acid is (are) ______.

Two possible stereo-structures of ${\text{CH}}_{\text{3}}\text{CH(OH)COOH}$, which are optically active, are called ______.

Which of the following is an optically active compound?