Which one number is wrong in the given series? 126 139 128 138 130 135

This is an alternating series: Series 1 (odd positions): 126, 128, 130 (+2 pattern). Series 2 (even positions): 139, 138, 135 (should be 137 to maintain -1 pattern: 139-1=138, 138-1=137). The number 138 breaks the alternating pattern - the even position series should decrease by 1 each time, so after 138 should come 137, not 135. Thus 138 is the wrong number in its position.