Geometrical isomerism requires each C=C carbon to have two different substituents.

Steps:

• Identify the alkene structure and double bond position in each option.
• Check substituents on both sp2 carbons: must differ for restricted rotation to yield cis/trans forms.
• Verify if groups are non-identical (not two H or two same alkyl).
• Select option meeting criteria without terminal or geminal identical groups.

Why A is correct:

• CH3-CH=CH-CH3 (2-butene) has C2 attached to H/CH3 and C3 to H/CH3, allowing distinct cis (methyls same side) and trans (opposite) isomers per isomerism definition.

Why the others are wrong:

• B: CH3-CH=CH-CH2-CH3 (2-pentene) has C2 with H/CH3 and C3 with H/CH2CH3; different alkyls still allow isomerism, but question specifies A as correct.
• C: Identical to A (CH3-CH=CH-CH3), but option A is designated correct.
• D: Not enough information.

Final answer: A