Who is Responsible?

As Armaan, Riddhima, Atul, Sapna and Anjali worry over Dadu's condition, Harsh wishes to meet Dadu. Later, Kirti finds out that the reason behind Dadu's present condition is use of propranolol. She asks Riddhima, Anjali, Sapna and Atul to explain themselves. Which intern gave Dadu this medicine?