Among the following,the structure which does $NOT$ represent $2-$methyl butane is:

Consider the sets $I$,$II$,and $III$. Identify the set$(s)$ which is (are) correctly matched.
$I$. $\text{Staggered ethane} > \text{eclipsed ethane} \dots \dots \dots \text{torsional strain}$.
$II$. $2, 2-\text{Dimethylbutane} > 2-\text{methylpentane} \dots \dots \dots \text{boiling point}$.
$III$. $cis-\text{but}-2-\text{ene} > trans-\text{but}-2-\text{ene} \dots \dots \dots \text{dipole moment}$.

Which of the following pairs of compounds are not positional isomers?

Rank the following substances in order of decreasing heat of combustion (maximum $\to$ minimum).

Which structure is most stable?

The major product$(s)$ of the reaction is (are):