**Core Concept:** Chalazion is a non-infective inflammation of the meibomian gland, which is a type of sebaceous gland responsible for producing an oily fluid that nourishes and keeps the tears balanced. The obstruction of this gland leads to the formation of chalazion.

**Why the Correct Answer is Right:** The correct answer, "C. Meibomian gland," highlights the primary cause of chalazion: obstruction of the meibomian gland. The meibomian gland is crucial for maintaining tear balance, and when obstructed, it results in a non-infective inflammation called chalazion.

**Why Each Wrong Option is Incorrect:**

A. **Option A (obstruction of lacrimal gland):** The lacrimal gland is responsible for producing the aqueous component of tears, not the oily component produced by the meibomian gland. Therefore, it is incorrect to associate lacrimal gland obstruction with chalazion formation.

B. **Option B (obstruction of eyelid margin):** Although eyelid margin obstruction can lead to some conjunctival hyperemia, it is not the primary cause of chalazion. The chalazion is solely due to meibomian gland obstruction.

D. **Option D (obstruction of sebaceous gland):** While sebaceous glands are important for skin lubrication, their obstruction does not result in chalazion formation, as chalazion is specifically related to meibomian gland obstruction.

**Clinical Pearl:** A thorough understanding of the anatomy and function of the different glands in the eyelid is essential for recognizing and accurately diagnosing chalazion. This differentiation is crucial for appropriate management strategies, including physical examination methods and treatment options.