**Core Concept**
The question tests the association of anti-tubercular drugs with psychiatric side effects, specifically psychosis. Isoniazid, a first-line antitubercular agent, is known to cause a range of neurological and psychiatric side effects.

**Why the Correct Answer is Right**
Isoniazid is associated with psychosis due to its mechanism of action as an inhibitor of pyridoxal phosphate, a form of vitamin B6. This leads to a decrease in the levels of neurotransmitters such as serotonin, dopamine, and norepinephrine in the brain, which can cause psychiatric symptoms including psychosis. The pyridoxine deficiency caused by isoniazid can also lead to seizures, peripheral neuropathy, and other neurological side effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Rifampicin is known for its hepatotoxicity and is not commonly associated with psychosis.
**Option B:** Ethambutol can cause optic neuritis, leading to visual disturbances, but it is not typically linked to psychosis.
**Option C:** Pyrazinamide is associated with hepatotoxicity and arthralgias, but it is not commonly linked to psychosis.

**Clinical Pearl / High-Yield Fact**
Isoniazid-induced psychosis can be prevented or treated with pyridoxine supplementation, highlighting the importance of monitoring for and managing vitamin B6 deficiency in patients taking isoniazid.

**Correct Answer:** C. Isoniazid.