<prompt> Most common site for impaction of gell stones in gall stone lieus is :Ist pa of duodenumIInd pa of duodenumTerminal ileumColon  <response>: Answer is C Terminal ileum:Classically there is obstruction impaction about 60 cm proximal to ileocaecal valve- BaileyThe site of obstruction by the impacted gall stone is usually at the ileocaecal valve provided that the more proximal S.I. is of normal calibre. - HarrisonsIf both choices come simultaneously in a question go for 60 cm proximal to ileacoecal valve, as, it has been defined as the narrowest pa of small intestine. 