A) This is a (4 2) reflection.
B). . .
The planes indicated are parallel to the (2 1) set of planes but have half the d-spacing of the (2 1) planes. The (2 1) planes would be the set parallel to the ones shown, but with none of the planes empty of lattice points.
C) This is a second order Bragg reflection, the order n being the largest common divisor of the (h k) indices.