Number of possible cyclic isomers (including with stereo isomer) for the molecular formulae C₅H₁₀ is

Among the cyclic isomers of the compound, in order to find the stereoisomers, the carbon with the chiral centre is needed to be identified. Then with respect to the chiral carbon, we can find the other isomers.

Degree of unsaturation, D.U. = $C - \frac{H}{2} + 1$

now, $D{U}_{C_5{H}_{10}} = 5 - \frac{10}{2} + 1 = 1$

As the DU is 1, it means that either there is one ring or one unsaturation i.e. double bond. However, we will find the cyclic or ring structures only (according to the questions).

Now, we can form either a 3, 4 or maximum 5 membered ring.

So, there are total 7 cyclic isomers (including stereoisomers) of C₅H₁₀