Section 2(6)(a) in Bihar (In Admission In Educational, Institutions) Reservation Act, 2003
(a)After providing the opportunity for admission to the candidates having descending order of merit of Lower qualification as to marks obtained etc. fixed by the concerned educational Institutions, it the reservation percentage of any reserved category is not filled shall be regulated in the following manner:-(i)Exchange shall be possible between the Scheduled Castes and Scheduled Tribes.(ii)Exchange shall be possible between the Extremely Backward Classes and Backward Classes.