Explanation:
(a) The necessary and sufficient condition for a compound to exhibit geometrical isomerism is that the two groups attached to the same carbon must be different, i.e., alkenes of the following types show cis-trans isomerism.
\(a b \mathrm{C}=\mathrm{C} a b, a b \mathrm{C}=\mathrm{C} c d, a b \mathrm{C}=\mathrm{C} a x\),
\(a b \mathrm{C}=\mathrm{C} b x\)
Thus, out of the given examples, only but-2-ene exhibits geometrical isomerism.
cis-isomer
trans-isomer