Final answer:
The most valid remarketing audience for a remarketing list for search ads campaign would be option 1) users who have visited the website in the past 30 days, as they are more likely to engage with the ads and convert into customers.
Step-by-step explanation:
For a remarketing list for search ads campaign, it is important to include users who have shown previous interest in the website. Therefore, the most valid remarketing audience would be option 1) users who have visited the website in the past 30 days, as they are more likely to engage with the ads and convert into customers.
On the other hand, users who have made a purchase in the last 6 months (option 2) may already be existing customers and may not need to be remarketed to.
Similarly, users who have clicked on a specific ad in the last week (option 3) may have already engaged with the ad and taken the desired action, so remarketing to them may not yield optimal results.
Lastly, users who have never visited the website before (option 4) have no previous interaction with the website, so it would be less likely for them to convert into customers through remarketing.