In a report showing users from different device types, which of the following represents a "metric" in Google Analytics?

In Google Analytics, a "metric" is a quantitative measurement that reflects certain aspects of user interactions or behaviors. The correct choice pertains to the total number of users on a specific device category, which is indeed a metric since it can be measured and expressed as a number.

Looking at the options, the average session duration on mobile and the bounce rate are both derived values that provide insights into user engagement and behavior but do not represent direct counts. They are considered derived or calculated metrics rather than direct metrics themselves. While the total number of new users on desktop does quantify user interactions, it is focused on a specific category (new users) rather than a holistic measure like total users on mobile.

The distinction lies in the directness of measurement; "how many users were on mobile phones" is viewed as a straightforward tally of mobile users, making it a clear metric in Google Analytics.