Expression : XYXYXYxy, XYXYXyxY, XYXYxyXY, XYXyxYXY, XYxyXYXY, _______________. The pattern followed is that in each term there are 4 combinations of 'XY' and in each term, the last two terms in decreasing order are small alphabets. Thus, in the missing term, the second and third term will be small = XyxYXYXY