An experimental investigation has been carried out to study the mixing promoting efficiency of right-angled and isosceles triangular tabs with sharp and truncated vertices. The mixing promotion caused by two identical triangular tabs, offering a geometrical blockage of 2.5% each, placed at the exit of a Mach 2 circular nozzle, was studied in the presence of adverse and marginally favourable pressure gradients. The results of the present study demonstrate the validity of the hypothesis that, the triangular tabs shedding vortices of continuously varying sizes is a better mixing promoter than the rectangular tabs, shedding vortices of uniform size. Furthermore, the truncated vertex triangular tab is found to be a better mixing promoter than the sharp vertex triangular tab, at all levels of expansion of the present study.