What determines whether a Search ad shows in the results for a query, and in what position?

The selection is correct because Ad Rank is the definitive metric Google uses to determine an ad's eligibility and its specific placement on the search results page. Rather than relying on a single factor like a high bid, Ad Rank is a complex calculation that balances the advertiser's maximum bid with several quality-based components, including the Expected Click-Through Rate (eCTR), Ad Relevance, and Landing Page Experience. Furthermore, Ad Rank accounts for the Ad Rank thresholds required for a specific position, the context of the user's search (such as device, location, and time of day), and the expected impact of assets like sitelinks or images. By using this multi-faceted approach, Google ensures that the auction rewards ads that are not only financially competitive but also highly useful and relevant to the user's intent, maintaining a high-quality experience for both searchers and advertisers.