Same keyword in two different ad groups, which one will win the auction?

If an advertiser has the same keyword in two different ad groups, the one to win a given auction will be the keyword with the:

• Most historical data in the account.
• Highest Ad Rank.
• Highest maximum cost-per-click (CPC) bid.
• Best Quality Score.

The correct answer is:

• Best Quality Score.

Explanation: 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.

You can read more here: https://support.google.com/Google Ads/answer/2756257?hl=en