Step 1: Define the entity. Alcoholic paranoia, also called alcohol-induced delusional disorder, is a chronic alcohol-related psychosis dominated by delusions, classically delusions of jealousy or infidelity (pathological jealousy, the Othello syndrome).
Step 2: Identify the hallmark. Its defining feature is fixed, persistent delusions, usually of marital infidelity, held with firm conviction.
Step 3: Separate it from look-alikes. Prominent hallucinations point instead to alcoholic hallucinosis, a different disorder, so hallucinations are not the marker here. Drowsiness suggests intoxication or sedation, not a paranoid delusional state. Impulsive agitation describes withdrawal or delirium, not the stable delusional theme of alcoholic paranoia.
Step 4: Match to the options. The feature that uniquely belongs to alcoholic paranoia is fixed delusions.
Step 5: Therefore the answer is fixed delusions.
Answer: Fixed delusions.