In geometric isomers, the terms cis and trans refer to:

The correct choice is centered on the arrangement around a double bond, which is the defining characteristic of geometric isomers. In geometric isomerism, specifically when discussing the terms "cis" and "trans," we are referring to the spatial orientation of substituents attached to the carbon atoms involved in a double bond.

In a cis isomer, similar or identical groups are on the same side of the double bond, whereas in a trans isomer, these groups are on opposite sides. This difference in spatial arrangement can lead to distinct physical and chemical properties despite the presence of the same molecular formula, highlighting the significance of geometry in determining molecular behavior.

The other options do not accurately describe what cis and trans refer to in the context of geometric isomerism. Different angles between bonds relate more to the overall molecular shape and geometry rather than specifically to cis or trans arrangements. Functional groups' positions may pertain to structural isomerism but do not define geometric isomers as cis and trans does. Likewise, while isomerization is a broader term that encompasses various types of isomer changes, it doesn't specifically pinpoint the distinction made by cis and trans in geometric isomerism.