Coplanar points are three or more points which lie in the same plane .A plane is a flat surface which extends without end in all directions. A set of points, lines, line segments, rays or any other geometrical shapes that lie on the same plane are said to be Coplanar.In the above figure given :Among all the options given a)C, H, E b)B, K, H c). A, B, K are not lying in the same plane .
Points A, E, D are lying in the same plane and hence are coplanar.
Option D is the right answer.