The value of $x$ in compound '$D$' is $.........$.

The list given below contains essential amino acids that are basic $(X)$ and also non-essential amino acids that are neutral $(Y)$. Identify $X$ and $Y$ from the following list:
$a)$ Lysine
$b)$ Alanine
$c)$ Serine
$d)$ Arginine
$e)$ Tyrosine

Which one of the following is the correct structure of cytosine?

The structure of $Gly-Ala$ is

Which of the following statements is/are true for amino acids?
$(A)$ The solubility of an amino acid in water is maximum at its isoelectric point $(pH)$.
$(B)$ It gives a ninhydrin test.
$(C)$ It releases nitrogen gas upon reaction with nitrous acid $(HNO_2)$.

$A$ protein undergoes reversible thermal denaturation from its initial state $N$ to denatured state $D$ according to $N \rightleftharpoons D$. At $60 ^\circ C$, the concentrations of both $N$ and $D$ are equal at equilibrium, and the standard enthalpy change of denaturation is $666 \text{ kJ mol}^{-1}$. The standard entropy change ($\Delta S^\circ$ in $\text{kJ K}^{-1} \text{mol}^{-1}$) of the protein upon denaturation at $60 ^\circ C$ is closest to