Can a structural isomer also be a geometric isomer?

Structural isomers.

1. hexane: CH3-CH2-CH2-CH2-CH2-CH3 2. 3-methylpentane: CH3-CH2-CH(CH3)-CH2-CH3 3. 2-methylpentane: CH3-CH(CH3)-CH2-CH2-CH3 4. 2,2-dimethylbutane: CH3-C(CH3(CH3))-CH2-CH3

In chemistry, isomers (from Greek ισομερης, isomerès; isos = "equal", méros = "part") are compounds with the same molecular formula but different structural formulas. Isomers do not...

Stereoisomers are isomeric molecules that have the exact same molecular formula, but a different three dimensional position. A conformer is a set of stereoisomers.

No, methane and ethane have no geometric isomers.