In order that a compound may show geometrical isomerism

A) Compound must have a chiral carbon
B) Each of the two doubly bonded carbon atoms must have different atoms or groups
C) Compound must have a plane of symmetry

C₁ and C₂ carbon groups can be or cannot be same.

Geometrical isomerism is not possible if C₁ or C₂ two groups are same.

So in the four group they exhibit.

$$\begin{gathered} {\mathrm{Ca}}_2 = {\mathrm{Cb}}_{2{ }_{ }} {}_{\mathrm{a}⋰}{}^{\mathrm{a}\ddots }\underset{1}{\mathrm{C}} ={\underset{2}{\mathrm{C}}}_{\ddots \mathrm{b}}^{⋰\mathrm{b}} \mathrm{No} \mathrm{geometrical} \mathrm{isomerism} \\ {\mathrm{Ca}}_{2 } =\mathrm{Cab} {}_{\mathrm{a}⋰}{}^{\mathrm{a}\ddots } \underset{1}{\mathrm{C}} = \underset{2}{{\mathrm{C}}_{\ddots \mathrm{b}}^{⋰\mathrm{a}}} \mathrm{No} \mathrm{geometrical} \mathrm{isomerism} \\ \mathrm{Cab} = \mathrm{Cab} {}_{\mathrm{b}⋰}{}^{\mathrm{a}\ddots }\mathrm{C} = {\mathrm{C}}_{\ddots \mathrm{b}}^{⋰\mathrm{a}} \mathrm{Exhibits} \mathrm{Geometrical} \mathrm{Isomerism} \end{gathered}$$it geometrical isomerism.