ABCDEFGH is a hol A. will be valid.

B. will not be valid since the ions would experience forces other than due to collisions with the walls.

C. will not be valid since collisions with walls would not be elastic.

D. will not be valid because isotropy is lost.

Here face ABCD has positive charge on it and inside the cube has ionized hydrogen. Due to the presence of positive charge on the face the hydrogen ions will experience forces other than the force due to collision on the walls of the cube. These forces must be electrostatic in nature and isotropy is lost at ABCD due to positive charge .Therefore, the usual kinetic theory expression for pressure is not valid.