Which statement about rem units is correct?

• A. Rem is relative to the root element's font size, whereas px is fixed in pixels.
• B. Rem is fixed and not affected by root font size changes; px scales with root.
• C. Rem and px both scale with zoom level identically
• D. Rem is relative to the element's own font size

Answer: (A)

Rem units are based on the root element’s font size, usually the html element. That means 1rem equals the root font size you set (for example, if html { font-size: 16px; } then 1rem = 16px, 2rem = 32px). Because rems scale with changes to the root font size, adjusting that size makes every rem-based measurement grow or shrink together, which is handy for accessibility and responsive design.

In contrast, pixels are an absolute length in CSS pixels. They don’t depend on the font size of elements; they’re fixed in the root reference and only visually change when you zoom the page. So the statement that rem is relative to the root font size and px is fixed in pixels captures the key distinction.