$2($a$)$ For a viscous steady$-$state laminar flow on top of a flat plate, a boundary layer is developed next to the plate.

$($i$)$ State the basic assumptions for the flows outside and inside the boundary layer, as well as for the boundary layer thickness.

$(5$ marks$)$

$($ii$)$ State the necessary boundary conditions for boundary layer flow and explain the physical meaning of each condition. Use sketches to denote variables if necessary.

$(5$ marks$)$