To show geometrical isomers, the groups attached to double bond should be different. There should be at least 2 different types of groups attached to it.

In 1^st all the groups are different, 2^nd and 3^rd have 2 different groups attached which are capable of showing cis and trans isomers.

But 4^th have 3 same groups attached to double bond. Thus (iv) will not be able to show geometrical isomerism.