This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anxiety disorders stress disorders and grief, Subject name: Psychiatry
Irresistible urge to do a thing repeatedly is seen in 
Select and explain. 
A. Obsessive - compulsive disorder, B. Schizophrenia, C. Schizoaffective disorder, D. Depression
A: Obsessive - compulsive disorder
Answer: A: Obsessive - compulsive disorder 
Explanation: An obsession is defined as an idea, impulse or image which intrudes into the conscious awareness repeatedly, patient tries to resist against it but is unable to . an obsession is usually associated with compulsion and a compulsion is defined as a form of behaviour which usually follows obsessions,the behaviour is not realistic and is either irrational or excessive compulsion may diminish the anxiety associated with obsession (Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no 95)