If you’re using remarketing to reach people who’ve used your mobile app, they see your ads:

  • while browsing and using Google Maps
  • each time they re-use your mobile app
  • when they enter search terms for products like yours on a mobile device
  • while using other mobile apps on the same mobile or tablet device

The correct answer is:

  • while using other mobile apps on the same mobile or tablet device

Explanation: Remarketing lets you show ads to people who have visited your website or used your mobile app before. When people leave your website without buying anything, for example, remarketing helps you reconnect with them by showing relevant ads as they browse the web, as they use mobile apps, or as they search on Google.

Remarketing for mobile apps: Show ads to people who have used your mobile app or mobile website as they use other mobile apps or browse other mobile websites

Read more here: https://support.google.com/adwords/answer/2453998?hl=en