At normal temperature,$X$ and $Y$ are:

If a carbon atom is attached to $-H, -OH, -COOH$ and $-OCO^{-}C_2H_5$ groups,the number of chiral $C$ atoms in the molecule is:

What is the absolute configuration of the following molecules? ($NS =$ the molecule has no stereocenter) Note: For the purpose of this question only,the order of stereocenters is not specified; i.e.,$R, S = S, R$.
$(I)$ || $(II)$ || $(III)$ || $(IV)$

Among the structures shown below,which has the lowest potential energy?

Which structure is most stable?

In which of the following is the keto form more dominating than the enol form?