**Core Concept**
The question is testing the student's knowledge of delusional disorders, specifically a type of delusion known as nihilistic delusion. Nihilistic delusion is a psychiatric symptom where the individual believes that nothing exists or that the world is going to end.

**Why the Correct Answer is Right**
Nihilistic delusion is a type of delusion that is often seen in schizophrenia and other psychotic disorders. It is characterized by a pervasive feeling of nothingness or a lack of meaning in life. The individual may believe that they are the only one who exists or that the world is going to end soon. This type of delusion is often accompanied by other symptoms such as hallucinations, disorganized thinking, and social withdrawal.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a specific type of delusion. While it is a possible symptom of various psychiatric disorders, it is not a distinct category of delusion.

**Option B:** This option is incorrect because it is a type of delusion that involves a false belief in one's own identity or role, rather than a belief that nothing exists.

**Option C:** This option is incorrect because it is a type of delusion that involves a false belief in one's own identity or role, rather than a belief that nothing exists.

**Clinical Pearl / High-Yield Fact**
A key feature of nihilistic delusion is that it is often accompanied by a sense of hopelessness and despair. This can make it challenging for clinicians to treat, as the individual may be resistant to therapy and may require a more supportive approach.

**Correct Answer:** C. Nihilistic delusion.