Western Governors University (WGU) ITWD3120 C777 Web Development Applications Practice Exam

Using a percentage to specify the width of an image in responsive web design allows the image to scale relative to its parent container. This is a crucial aspect of responsive design, as it ensures that images resize appropriately on different screen sizes and devices.

When an image is set to a percentage width, it occupies a portion of its parent's width, maintaining its aspect ratio while adjusting to various screen dimensions. This adaptability improves the user experience on mobile and desktop platforms since it helps prevent overflow or distortion.

In contrast, using fixed units like pixels (px) would lock the image size, potentially leading to layout issues on varying screen sizes. Other options such as "pc" (picas) and "#" (which typically denotes an id selector in CSS) do not pertain to specifying image width in the context of responsive design. Therefore, the percentage value is the most effective choice for achieving fluid layouts that enhance accessibility and usability across diverse devices.