A parametric study to investigate the effects of magnetic field, chemical reaction, thermal radiation, thermal diffusion (Soret effect) and diffusion – thermal (Dufour effect) on a free and forced convective fully developed boundary layer mass transfer flow of an electrically conducting viscous incompressible optically thick fluid past a semi-infinite vertical porous plate is presented. A magnetic field of uniform strength is assumed to be applied normal to the plate directed into the fluid region. The non-linear partial differential equations, governing the flow and heat and mass transfer have been transformed by a similarity transformation into a system of non-linear ordinary differential equations. The resulting system of ordinary non-linear differential equation is then solved numerically by adopting shooting method. The profiles of the dimensionless velocity, temperature and concentration distributions are demonstrated graphically for various values of the parameters involved in the problem.Finally, the corresponding local skin-friction co-efficient, local Nusselt number and local Sherwood number are also presented in tabular form. Some of the results of the present work are compared with that of Alam et al.  and found to be in good agreement.
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