**Core Concept**
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain, altered bowel habits, and mucus passage without detectable structural or biochemical abnormalities. It is commonly triggered by stress and is diagnosed clinically based on symptom patterns and exclusion of organic causes.

**Why the Correct Answer is Right**
Irritable bowel syndrome (IBS) presents with recurrent abdominal pain associated with changes in bowel habits, such as diarrhea, constipation, or both, and passage of mucus—without blood or inflammation. The symptoms are often worsened by stress, and there is no evidence of intestinal damage or infection. The diagnosis is made using the Rome criteria, which emphasize symptom duration and pattern, with no abnormal lab or imaging findings. This matches the patient’s presentation perfectly.

**Why Each Wrong Option is Incorrect**
Option B: Ulcerative colitis involves continuous colonic inflammation, typically with bloody diarrhea, weight loss, and systemic symptoms. Blood in stool is a hallmark, which is absent here.
Option C: Crohn’s disease affects any part of the GI tract, presents with bloody diarrhea, perianal disease, and systemic signs, and is confirmed by imaging or biopsy—none of which are present.
Option D: Amebiasis causes dysentery with blood and mucus, fever, and often a history of travel or exposure. It is diagnosed by stool microscopy or antigen testing and is not stress-related.

**Clinical Pearl / High-Yield Fact**
In IBS, pain is often relieved by defecation and is linked to visceral hypersensitivity. Stress exacerbates symptoms, and the absence of blood, fever, or inflammation is key to differentiating it from inflammatory bowel disease.

✓ Correct Answer: A. Irritable bowel syndrome