Total number of possible isomers (both structural as well as stereoisomers) of cyclic ethers of molecular formula ${\text{C}}_4{\text{H}}_8\text{O}$ is :

For the molecular formula ${\text{C}}_4{\text{H}}_8\text{O}$, the possible cyclic ethers (including structural and stereoisomers) are:Tetrahydrofuran: 1 isomer.2-methyloxetane: Chiral center at C2, so 2 isomers ($R$ and $S$).3-methyloxetane: 1 isomer.Ethyloxirane: Chiral center, so 2 isomers ($R$ and $S$).2,2-dimethyloxirane: 1 isomer.2,3-dimethyloxirane: Can exist as cis (meso) and trans (enantiomeric pair). Total: 3 isomers.Summing these up: $1+2+1+2+1+3=10$ isomers.