$20*$

$1$ point

The four molecules listed below that are isomers of $Cs{H}_{10}(l)$ are numbered $,$ and $($Record all four digits of your answer in numerical order$)$

Molecules

$1$ pent$-2-$ene

$2$ pent$-2-$yne

$3$ cyclopentane

$4$ methylpropane

$5$ dimethylpropane

$6$ ethyleyclopropane

$7.$ methylcyclobutanc