**Core Concept**
In the management of acute exacerbation of ulcerative colitis, the primary goal is to induce and maintain remission. The treatment involves a combination of aminosalicylates, corticosteroids, immunomodulators, and biologics. Aminosalicylates, such as sulfasalazine, are effective in mild to moderate cases, while corticosteroids are used for moderate to severe cases.

**Why the Correct Answer is Right**
The correct answer is a corticosteroid, specifically **Prednisolone**. Corticosteroids work by reducing inflammation in the gastrointestinal tract. They inhibit the production of pro-inflammatory cytokines, such as TNF-alpha, and induce anti-inflammatory cytokines like IL-10. This leads to a decrease in the severity of symptoms and induction of remission in ulcerative colitis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Sulfasalazine is an aminosalicylate, which is effective in mild to moderate cases of ulcerative colitis but not in acute exacerbations.
* **Option B:** Infliximab is a biologic agent that targets TNF-alpha and is used in moderate to severe cases of ulcerative colitis, but it is not the first-line treatment for acute exacerbation.
* **Option D:** Mesalamine is another aminosalicylate that is used in mild to moderate cases of ulcerative colitis, but it is not effective in acute exacerbations.

**Clinical Pearl / High-Yield Fact**
In patients with ulcerative colitis, corticosteroids should be tapered gradually to avoid rebound inflammation. A common approach is to start with a high dose of prednisolone (40-60 mg/day) and taper it by 5-10 mg every 2-3 days.

**Correct Answer:** C. Prednisolone