Which prefix would indicate a fractional quantity?

The prefix that indicates a fractional quantity is "semi-." This prefix comes from Latin and is commonly used in medical terminology, meaning "half" or "partial." When attached to a word, it signifies that something is only partially present or is at a fractional level. For example, the term "semipermeable" refers to a membrane that allows certain substances to pass through while restricting others, illustrating the concept of partial permeability.

While other prefixes such as "re-," "pseudo-," and "sub-" have their own distinct meanings, they do not convey the idea of a fractional quantity. "Re-" often suggests repetition or return to a previous state; "pseudo-" denotes something that is false or deceptive; "sub-" indicates something that is below or under, but not specifically fractional. Hence, "semi-" is the clear choice when discussing fractional quantities.