Which of the following will not cause a cloud on the title to real estate?

A pending zoning change does not create a cloud on the title to real estate because it is merely a proposed change in land use regulation that has not yet been enacted. It doesn't affect the current ownership status or legal rights associated with the property until it is actually approved and implemented.

In contrast, unpaid property taxes can lead to a lien against the property, creating a significant obstacle for the title. Similarly, litigation involving the property can cloud the title since it reflects ongoing legal disputes that could affect ownership or use. Unrecorded claims also present a problem, as they can represent potential rights or interests in the property that have not been officially documented, potentially leading to uncertainty about ownership rights. Thus, the nature of a pending zoning change is such that it does not constitute a legal claim or issue affecting the title directly, distinguishing it from the other options presented.