Which of the following will have one of the stereoisomers as a meso compound?

The number of isomers of $C_5H_{12}$ is:

How many isomers have the molecular formula $C_6H_{11}Br$ and are derivatives of cyclopentane? (ignoring chirality)

Assertion $A$: Enol form of acetone $[CH_{3}COCH_{3}]$ exists in $< 0.1 \%$ quantity. However,the enol form of acetylacetone $[CH_{3}COCH_{2}COCH_{3}]$ exists in approximately $15 \%$ quantity.
Reason $R$: Enol form of acetylacetone is stabilized by intramolecular hydrogen bonding,which is not possible in the enol form of acetone. Choose the correct statement:

The pair of metamers is :-

What do the following pairs of structures represent?