**Core Concept**
The question requires the identification of the most effective pharmacological agent for managing acute exacerbations of ulcerative colitis, a type of inflammatory bowel disease (IBD). This involves understanding the pathophysiology of ulcerative colitis and the mechanism of action of various medications used in its treatment.

**Why the Correct Answer is Right**
The correct answer is **B. Infliximab**. Infliximab is a monoclonal antibody that targets tumor necrosis factor-alpha (TNF-alpha), a key cytokine involved in the inflammatory process of ulcerative colitis. By binding to TNF-alpha, infliximab reduces inflammation and promotes healing in the gastrointestinal tract. This mechanism of action has been shown to be effective in inducing and maintaining clinical remission in patients with moderate to severe ulcerative colitis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because corticosteroids, such as prednisolone, are not the first-line treatment for acute exacerbations of ulcerative colitis due to their limited effectiveness and potential side effects.
* **Option C:** This option is incorrect because aminosalicylates, such as sulfasalazine, are primarily used for maintaining clinical remission in mild to moderate ulcerative colitis and are not effective in inducing remission in acute exacerbations.

**Clinical Pearl / High-Yield Fact**
Infliximab is a biologic agent that has revolutionized the treatment of inflammatory bowel disease, particularly in patients who have failed conventional therapies. It is essential to recognize the indications and contraindications for biologic agents, such as infliximab, and to monitor patients closely for potential side effects.

**Correct Answer: B. Infliximab**