The $IUPAC$ name of the following compound is:

Fill in the blanks:
$(1)$ The $IUPAC$ name of $CH_3COCH_2CH_2CH_2COOH$ is .........
$(2)$ The formula of pent$-4-$en$-2-$ol is .........
$(3)$ The $IUPAC$ name of the following structure is ......... and ......... is the main functional group in it.
(Structure: $A$ cyclohexene ring with an $-OH$ group attached to the carbon adjacent to the double bond,such that the double bond is between carbons $2$ and $3$ relative to the $-OH$ at position $1$.)
$(4)$ For $CH_3CH(OH)CH_2CH_2CH_2CHO$,the main functional group and the second priority group are ......... and ......... respectively.

Give the structure of the $neo$-pentyl group.

Which of the following is the correct order of priority for groups in $R-S$ nomenclature?

What is the common name of $2, 3$-dihydroxybutanedioic acid?

For the organic compound $CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3$,at which carbon atom should a substitution occur to make the compound chiral?