constitutional isomers

How many possible constitutional isomers of cycloalkane having the molecular formula C5H10?

4 constitutional isomers :
cyclopentane
methylcyclobutane
ethylcyclopropane
dimethylcyclopropane (a pair of geometrical isomers)

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How many possible constitutional isomers having the molecular formula C6H14?

5 constitutional isomers :
hexane
2-methylpentane
3-methylpentane
2,2-dimethylbutane
2,3-dimethylbutane

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How many possible constitutional isomers of alkene having the molecular formula C5H10?

6 constitutional isomers :
pent-1-ene
pent-2-ene
2-methylbut-1-ene
3-methylbut-1-ene
2-methylbut-2-ene
2,2-dimethylpropene

I DON'T KNOW~~