Which of the following is not a standard dimension in Google Analytics?

Cost per Acquisition is not a standard dimension in Google Analytics because it represents a calculated metric rather than a dimension. In Google Analytics, dimensions are attributes of your data, such as the geographic location of your users (City), the titles of the pages they visit (Page Title), or where they came from (Source/Medium). These elements provide context for the data collected and can be used to segment traffic and analyze user behavior.

On the other hand, Cost per Acquisition is a metric that reflects the total cost of acquiring a customer divided by the number of conversions. This calculation uses standard dimensions to derive the result, but it does not function as a standalone dimension itself. Thus, it falls into the category of metrics rather than dimensions. Understanding the distinction between dimensions and metrics is crucial for proper reporting and analysis in Google Analytics.