Which of the following is NOT a fluid measurement?

The correct answer identifies pixels (px) as the option that is NOT a fluid measurement. In the context of web design and development, fluid measurements refer to units that allow for flexible and responsive layouts, adapting to different screen sizes and resolutions.

Pixel (px) is a fixed unit of measurement, meaning it represents a specific number of pixels on the screen. When you set dimensions in pixels, those dimensions do not change regardless of the viewport size; they stay consistent, leading to fixed layouts. This can create issues on different devices, as the content may not scale appropriately or may become inaccessible or poorly formatted on smaller screens.

In contrast, percentage (%) is a fluid measurement that allows elements to scale based on the parent container’s size. Relative units like rem (root em) and em also serve as fluid measurements because they adjust based on the font size of the parent or root element, respectively, allowing for more responsive and adaptable designs. These units are essential for creating flexible layouts that can accommodate a range of display sizes while maintaining usability and design integrity.