Assertion (A): Suitable method for preparation of primary amine is when haloalkane is treated with excess of ${\mathrm{NH}}_3$.

Reason (R): In this reaction primary, secondary, tertiary amines are formed.

Hydrolysis of sucrose brings about a change in sign of rotation from dextro $(+)$ to Laevo $(-)$ and such a sign change is known as -

In $\mathrm{\beta }$ -sheet of proteins, conformers are held together by (Secondary structure of protein) which forces?

$\mathrm{DNA}$ contains following purines bases -

$\left(\mathrm{a}\right)$ Adenine
$\left(\mathrm{b}\right)$ Guanine

$\left(\mathrm{c}\right)$ Thymine
$\left(\mathrm{d}\right)$ Cytosine