What is the default display value for a <div> element?

The default display value for a <div> element is block. This means that a <div> will take up the full width available to it and start on a new line, creating a block-level structure in the layout of a webpage. Block elements are typically used to define larger sections of a page, allowing for content to be arranged in a vertical stack. This behavior is important for structuring HTML documents since it gives web designers control over the flow of content, making it easier to create visually distinct sections.

The other options represent different types of display properties. Inline elements, for example, do not start on a new line and only take up as much width as necessary, while inline-block elements allow for block-like margins and padding but still sit inline with other elements. The flex property is used in flexbox layouts to enable flexible, responsive design but is not the default for divs. Understanding these differences is key when working with CSS to layout elements effectively on a webpage.