In order that a compound show geometrical isomerismA)    Compound must have a chiral carbonB)    Each of the two doubly bonded carbon atoms must have different atoms or groupsC)    Compound must have a plane of symmetry

Conclusion:→ In order to exhibit geometrical isomerism, double bonded carbon should possess two different groups.→ The C1 carbon two groups and C2 carbons two groups may (or) may not be same.→ Either C1 carbon two groups (or) C2 carbon two groups are identical then geometrical isomerism is not possibel.→ If all the four groups are different [a,b,c,d], then they donot exhibit CIS, trans isomerism but they exhibit geometrical isomerism i.e., E, Z-isomerism