Which prefix indicates "abnormal" conditions?

The prefix that indicates "abnormal" conditions is "para-." This prefix is often used in medical terminology to describe situations or conditions that are alongside or near the usual or normal state, hence suggesting an abnormality or deviation from the expected condition. For instance, terms like "paralysis" (loss of movement) or "parathyroid" (located beside the thyroid) highlight its association with abnormal development or function.

In contrast, the other prefixes do not signify an abnormality. "Post-" typically indicates something that occurs after a specific event or time. "Peri-" refers to something that surrounds or is around a certain structure. "Primi-" is used to denote the first occurrence, such as in "primigravida," which describes a woman who is pregnant for the first time. Each of these prefixes has distinct meanings, making "para-" the appropriate choice for indicating abnormal conditions.