In which scenario would ticket-splitting likely occur?

Ticket-splitting is a voting behavior wherein an individual votes for candidates from different political parties for different offices on the same ballot. The scenario where a voter supports a mayor from one party while also choosing a governor from another party exemplifies this behavior perfectly. It demonstrates the voter's willingness to evaluate candidates based on their individual platforms or qualifications rather than solely adhering to party lines.

In contrast, a party convention that endorses a single presidential candidate indicates a unified party approach, which discourages ticket-splitting, as participants are rallying behind a single candidate. Similarly, while a state electing a governor from a different party than the president does present scenarios for ticket-splitting, it highlights results rather than individual voter behavior. Lastly, a candidate winning both party nominations suggests a strong appeal across party lines but does not involve the decision-making process typical of ticket-splitting. Thus, the best representation of ticket-splitting is found in the first scenario where voters actively mix their party preferences across different offices.