<prompt> 2nd Most Common Hb in adult isa 2 ss 2a 2 g 2a 2 d 2ss 2 g 2  <response>: a 2 ss 2 is the most abundant Hb in adult About 2.5 of the hemoglobin is hemoglobin A2, in which b chains are replaced by d chains a2d2 which is second most abundant Hb in adult humanRef: Ganongs Review of Medical Physiology Twenty-Third Edition Page No: 522 