What is BPSC exam row that has caused a stir in Bihar & why is Prashant Kishor on hunger strike?

Over five lakh candidates took the Combined Competitive Exams on December 13, but allegations of a question paper leak led to protests in Patna. While fresh exams for 10,000 candidates were scheduled, Prashant Kishor began a hunger strike demanding cancellation, a domicile policy, and reforms.