Total number of isomers of $C_6H_{14}$ are

In the reaction,as shown in the image,the number of possible isomers for the organic compound $X$ is

For which of the following parameters would the structural isomers $C_2H_5OH$ and $CH_3OCH_3$ be expected to have the same values? (Assume ideal behavior)

Which one of the following isomeric structures has the lowest energy?

The type of isomerism between $CH_2Cl-CH_2Cl$ and $CH_3CHCl_2$ is ..........

Which among the given molecules can exhibit tautomerism?