This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Symptoms & Signs , Subject name: Psychiatry
A 32 year old female starts developing suspicion on her husband of having an affair with his secretory for 2 weeks. Diagnosis is? 
Select and explain. 
A. Illusion, B. Delusion, C. Hallucination, D. Delirium
B: Delusion
Answer: B: Delusion 
Explanation: Ans is 'b' i.e. Delusion * Above is an example of delusion of infidelity (morbid jealousy, Othello syndrome) i.e. False belief that one's lover has been unfaithful* A delusion is false, firm (unshakeable) belief that is not accepted by other members of patient's culture and society.