**Core Concept**
The patient has undergone Billroth II gastrectomy, a surgical procedure that involves resecting the stomach and reconnecting the remaining stomach to the jejunum (a part of the small intestine). This can lead to complications such as bile reflux gastritis, where bile flows back into the stomach, causing inflammation and irritation.

**Why the Correct Answer is Right**
The patient's symptoms of postprandial pain and oedematous, inflamed gastric mucosa are consistent with bile reflux gastritis. This occurs due to the abnormal flow of bile from the bile duct into the stomach, causing irritation and inflammation of the gastric mucosa. The reconnection of the stomach to the jejunum in Billroth II gastrectomy can lead to this abnormal bile flow.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that patients who have undergone Billroth II gastrectomy are at risk of developing bile reflux gastritis due to the abnormal flow of bile into the stomach. This can be a challenging diagnosis to make, as the symptoms may be similar to those of other conditions, such as peptic ulcer disease.

**Correct Answer:** B. Bile reflux gastritis