The stability analysis of trihybrid nanofluid (Cu/Ag/ A l 2 O 3 as nanoparticles and H 2 O as base fluids) with spherical, brick, and cylindrical shapes, respectively, are examined theoretically and analytically with throughflow. Normal mode techniques have been used for linear stability analysis, and truncated Fourier series is carried out for nonlinear analysis. Comparison of Hele-Shaw cell and Square enclosure is performed in both linear and nonlinear analysis. Square enclosures are found to prevail in heat and mass transfer. Hele-Shaw number (HS number) has destabilizing behavior. Increase in concentration of nanoparticle increases the heat and mass transfer. Cylindrical shapes particles are found to have earlier rate of convection in both the system. Furthermore, throughflow exhibits destabilizing behavior. Hele-Shaw cell prevail heat and mass transfer on comparing for regular fluid. In all the three phases Prandtl number enhances the heat/mass transfer due to increase in momentum diffusivity of the fluid.