**Core Concept**
Type-I lepra reaction, also known as reversal reaction, is an inflammatory response that occurs in the skin and peripheral nerves of patients with tuberculoid leprosy. It is a benign but potentially debilitating condition that can lead to nerve damage and disfigurement.

**Why the Correct Answer is Right**
Type-I lepra reaction is most commonly seen in patients with tuberculoid leprosy, a form of leprosy characterized by a strong cell-mediated immune response against the leprosy bacillus. This reaction typically occurs within the first 2 years after diagnosis and is thought to be triggered by an increase in the immune response against the bacillus. The reaction is mediated by the release of cytokines, such as interferon-gamma, which activate macrophages and lead to inflammation and tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** While lepromatous leprosy is a form of leprosy, it is not commonly associated with Type-I lepra reactions. Lepromatous leprosy is characterized by a weak cell-mediated immune response, which makes it more susceptible to Type-II lepra reactions.
**Option B:** Erythema nodosum leprosum (ENL) is a Type-II lepra reaction, which is different from Type-I. ENL is a more severe and systemic reaction that occurs in patients with lepromatous leprosy.
**Option C:** Borderline leprosy is a form of leprosy that is intermediate between tuberculoid and lepromatous leprosy. While patients with borderline leprosy can experience Type-I lepra reactions, it is not the most common form of leprosy associated with this reaction.

**Clinical Pearl / High-Yield Fact**
To remember the difference between Type-I and Type-II lepra reactions, recall that Type-I reactions occur in patients with a strong immune response (tuberculoid leprosy) and are characterized by inflammation and tissue damage, while Type-II reactions occur in patients with a weak immune response (lepromatous leprosy) and are characterized by a more systemic and severe inflammatory response.

**Correct Answer:** C.