The enol form in which ethyl $3$-oxobutanoate exists is

What does the given pair of structures represent?

Give the name and structure of the following:
$(i)$ Chain isomers of pentane $(C_5H_{12})$
$(ii)$ Isomers of $C_3H_8O$
$(iii)$ Isomers of $C_3H_6O$
$(iv)$ Metamers in $C_4H_{10}O$

Which of the following molecules is achiral?

Which one of the following molecules does not show stereoisomerism?

The total number of cyclic structural as well as stereo isomers possible for a compound with the molecular formula $C_5H_{10}$ is