Ans: The slope of the velocity boundary layer is maximum near the leading edge of the flat plate.
The slope of the boundary layer is nothing but rate of change of velocity with respect to distance y from the boundary.
The velocity profile is drawn on the velocity 'u' vs distance 'y' as follows. It becomes more clear about steepness of the slope.
What can you do with this information?
Remember that the slope is highest near the leading edge which in turn causes maximum shear stress at the leading edge. To have less frictional losses it should be kept in mind that the shear stress should be minimized for better designs.