**Core Concept**
Thought disorders are a category of psychiatric symptoms characterized by abnormalities in the form, content, and tone of thought. Form of thought disorders refer to disturbances in the logical organization, coherence, and sequence of thoughts, often leading to difficulties in communication and social interactions.

**Why the Correct Answer is Right**
Disorders of form of thought typically include symptoms such as loosening of associations, tangential thinking, and derailment. These symptoms are often seen in schizophrenia, bipolar disorder, and other psychotic disorders. However, disorders of content of thought, such as delusions and hallucinations, are distinct from form of thought disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** Disorganized thinking is a disorder of form of thought, characterized by a lack of logical organization and coherence in thoughts.
**Option B:** Thought block is also a disorder of form of thought, where a person suddenly stops speaking or thinking in the middle of a sentence or thought.
**Option C:** Thought insertion is a disorder of content of thought, where a person believes that their thoughts are being inserted into their mind by an external force.

**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the key features of thought disorders is "SCOTTY": Schizophrenia (disorganized thinking), Content (delusions, hallucinations), Organization (loosening of associations), Tone (flat affect), and Yield (social withdrawal).

**Correct Answer: C. Thought insertion is a disorder of content of thought.**