<prompt> Periodic acid schiff stain shows block positivity in the following cells:MyeloblastsLymphoblastsMonoblastsMegakaryoblasts  <response>: In acute lymphocytic leukemia ALL, cells show a varied staining pattern with periodic acid schiff PAS stain. Lymphoblasts of ALL may show a coarse block pattern of activity, a finely diffuse pattern, or a combinations of the two patterns, or they may be negative. Cells from Burkitts lymphoma are generally negative. Ref: Hematology: clinical principles and applications, 2007, Page 401. 