How does UI differ from UX?

The distinction between UI (User Interface) and UX (User Experience) is indeed captured well by the chosen answer. UI is primarily concerned with the aesthetic and functional aspects of a product's interface — this includes elements like buttons, icons, spacing, and color schemes. Essentially, UI focuses on how products are visually presented and how users interact with these interface elements.

On the other hand, UX encompasses a broader scope that includes not only the visual elements but also the overall experience users have when interacting with a product. This involves understanding user behavior, conducting research to gather insights on user needs and pain points, and designing a seamless, pleasurable experience throughout a user's journey.

Highlighting this distinction is critical because it underscores that while UI might make a product attractive and usable, UX ensures that the product is enjoyable and meets user expectations comprehensively. The other options misrepresent these concepts, linking UI with technical and coding aspects or usability testing, which do not accurately capture the essence of either term.