**Core Concept**
Bronchogenic carcinoma, especially small cell and adenocarcinoma subtypes, frequently causes hypercalcemia due to the release of osteoclast-activating factor (OAF) or parathyroid hormone-related protein (PTHrP), which stimulates bone resorption and increases serum calcium levels.

**Why the Correct Answer is Right**
In advanced bronchogenic carcinoma, tumor cells secrete PTHrP, which mimics parathyroid hormone and activates osteoclasts. This leads to increased bone breakdown, releasing calcium into the bloodstream. The resulting hypercalcemia is a hallmark of malignancy-associated hypercalcemia and is often accompanied by symptoms like polyuria, nausea, vomiting, and altered sensorium—consistent with this patient’s presentation. It is typically a late feature of cancer progression and can be life-threatening if untreated.

**Why Each Wrong Option is Incorrect**
Option A: Hypokalemia is not a typical feature of bronchogenic carcinoma. While some tumors may cause hypokalemia due to metabolic disturbances, it is not associated with hypercalcemia or the classic triad of symptoms.
Option B: Hyperkalemia is rare in lung cancer and usually occurs in renal failure or with certain drugs, not in malignancy-related hypercalcemia.
Option C: Hypocalcaemia is not seen in lung cancer; it is more common in conditions like hypoparathyroidism or vitamin D deficiency, and is not linked to tumor-induced bone resorption.

**Clinical Pearl / High-Yield Fact**
“PTHrP-secreting lung cancers cause hypercalcemia via bone resorption—remember the mnemonic: **‘Lung cancer → Hypercalcemia → PTHrP’**. This is a classic exam trap: do not confuse it with hypocalcemia or hypokalemia.”

✓ Correct Answer: D. Hypercalcemia