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:

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/adwords/answer/2756257?hl=en