**Core Concept**
Delirium is a complex neuropsychiatric syndrome characterized by disturbances in consciousness, attention, and perception. The underlying pathophysiology involves alterations in **neurotransmitter** systems, including **dopamine**, **serotonin**, and **acetylcholine**.

**Why the Correct Answer is Right**
The most common hallucinations in delirium are **visual hallucinations**, which occur due to the impaired regulation of **neurotransmitters** and altered **cortical** activity. This can lead to misperceptions and distorted sensory inputs, resulting in the patient seeing things that are not there.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **auditory hallucinations** are more commonly associated with **schizophrenia** and other **psychotic disorders**.
**Option B:** This option is incorrect because **tactile hallucinations** are less common in delirium and more often associated with **substance withdrawal**.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **visual hallucinations** are a hallmark of delirium, and their presence can help differentiate delirium from other **psychiatric** conditions.

**Correct Answer:** D. Visual hallucinations