The correct option is
D a-4; b-1; c-2; d-3
(a) Phobia is the intense fear of an object or a situation.
(b) Neurosis is a mental illness in which person suffers depression, obsessive behaviour, anxiety and feeling of unhappiness. These symptoms are maladaptive behaviour i.e. non productive and harmful.
(c) Hypochondria is a condition in which the person has undue concern about health. It occurs in adolescents with late development.
(d) Insomnia is lack of sleep. It can be due to anxiety, depression or other illness and medications.
So, the correct answer is 'a-4; b-1; c-2; d-3'.