**Core Concept**
Ghon's focus is a characteristic pathological feature of primary tuberculosis (TB), representing the initial site of infection in the lung. It is a granulomatous lesion that forms in response to the Mycobacterium tuberculosis bacterium.

**Why the Correct Answer is Right**
Ghon's focus typically develops in the right upper lobe of the lung, usually in the subpleural region. This is due to the fact that the right lung receives a greater volume of air, making it more susceptible to inhaled pathogens. The subpleural location is also favored by the anatomic structure of the lung, which allows for easier spread of the infection to the adjacent lymph nodes. The caesous lesion is a hallmark of Ghon's focus, characterized by caseous necrosis, a type of tissue destruction that is characteristic of TB.

**Why Each Wrong Option is Incorrect**
**Option A:** Ghon's focus is not typically located in the left apical parenchymal region, as the left lung is less susceptible to primary TB infection.
**Option B:** While the right lung is more commonly affected, Ghon's focus is not usually found in the apical parenchymal region, but rather in the subpleural region.
**Option D:** The left upper lobe is not the typical location for Ghon's focus, as the right upper lobe is more commonly affected.

**Clinical Pearl / High-Yield Fact**
Ghon's focus is often accompanied by an enlarged hilar lymph node, known as the Ghon's focus-hilar lymph node complex, which is a characteristic finding in primary TB. This complex is a key diagnostic feature that helps differentiate primary TB from other pulmonary infections.

**✓ Correct Answer: C. Sub pleural caesous lesion in right upper lobe**