(N/A) The $5^{th}$ member of the alkyne series follows the general formula $C_nH_{2n-2}$. For $n=6$,the molecular formula is $C_6H_{10}$.
The possible isomers are:
$(a)$ $HC\equiv C-CH_2-CH_2-CH_2-CH_3$: $Hex-1-yne$
$(b)$ $CH_3-C\equiv C-CH_2-CH_2-CH_3$: $Hex-2-yne$
$(c)$ $CH_3-CH_2-C\equiv C-CH_2-CH_3$: $Hex-3-yne$
$(d)$ $HC\equiv C-CH(CH_3)-CH_2-CH_3$: $3-Methylpent-1-yne$
$(e)$ $HC\equiv C-CH_2-CH(CH_3)-CH_3$: $4-Methylpent-1-yne$
$(f)$ $CH_3-C\equiv C-CH(CH_3)-CH_3$: $4-Methylpent-2-yne$
$(g)$ $HC\equiv C-C(CH_3)_2-CH_3$: $3,3-Dimethylbut-1-yne$
These isomers exhibit position isomerism (due to the change in the position of the triple bond) and chain isomerism (due to the difference in the carbon chain structure).