If an advertiser has the same keyword in 2 different ad groups, the one entered in a given auction will have the:
- highest Ad Rank
- lowest maximum CPC bid
- highest cost-per-acquisition (CPA) bid
- highest maximum cost-per-click (max. CPC) bid
The ad auction is how Google decides which ads to show and how they’re positioned. Your Ad Rank determines the ad position you win in the auction. Your Ad Rank is a score that’s based on your bid, auction-time measurements of expected CTR, ad relevance, landing page experience, and the expected impact of extensions and other ad formats.
When several broad match keywords in your ad group broadly match a search term, the system will prefer to use the keyword with the highest Ad Rank.
Read more here: https://support.google.com/Google Ads/answer/2756257?hl=en