**Core Concept**
Mendelson's syndrome is a condition that occurs in the context of anesthesia, characterized by chemical pneumonitis due to the aspiration of acidic gastric contents into the lungs. This aspiration can happen during the induction of anesthesia, when the protective reflexes of the airway are impaired, allowing stomach acid to enter the lungs.

**Why the Correct Answer is Right**
The aspiration of gastric contents into the lungs leads to an inflammatory response, causing damage to the alveoli and the bronchioles. The acidic nature of the gastric contents triggers a chemical pneumonitis, which can be severe and even life-threatening. The severity of the condition is directly related to the volume and pH of the aspirated gastric contents. The pathogenesis involves the direct toxic effects of the acidic gastric contents on the lung tissue, as well as an inflammatory response mediated by various cytokines and chemokines.

**Why Each Wrong Option is Incorrect**
**Option B:** Aspiration of nasal mucous is not related to Mendelson's syndrome, which specifically involves gastric contents. Nasal mucous aspiration can cause other complications, such as sinusitis or bronchitis, but it is not associated with the chemical pneumonitis characteristic of Mendelson's syndrome.
**Option C:** Hypersensitivity to inhalational anesthetics is not directly related to Mendelson's syndrome. While anesthetics can cause various side effects, hypersensitivity reactions are not a characteristic feature of this condition.
**Option D:** Faulty intubation syndrome is not a recognized medical condition. Faulty intubation can lead to various complications, including aspiration, but it is not a distinct syndrome that causes chemical pneumonitis.

**Clinical Pearl / High-Yield Fact**
To prevent Mendelson's syndrome, it is essential to ensure that the patient's airway is protected before the induction of anesthesia. This can be achieved by using a rapid sequence intubation (RSI) technique, which involves administering a muscle relaxant and an anesthetic agent in rapid succession to quickly secure the airway. Additionally, the patient should be positioned upright and receive a gastric tube to decompress the stomach before the induction of anesthesia.

✓ Correct Answer: A. Aspiration of gastric contents