Final answer:
The test technique being applied in evaluating a mobile banking app against user interface best practices is Checklist-based testing, where each element is verified against a predefined list of criteria.
Step-by-step explanation:
When testing a mobile app against a general list of user interface best practices, and evaluating each screen and field on each screen, the test technique being used can be best categorized as C. Checklist-based. This methodical approach involves verifying the app's features against predefined criteria or standards listed in a checklist, which is derived from user interface best practices. It is not exploratory testing, which would be more ad-hoc and unstructured, nor is it purely specification-based as it specifically relies on a general list of best practices rather than detailed functional specifications. Error guessing is also ruled out because it relies on the tester's experience to anticipate potential errors, rather than following a structured checklist.