I Why does (100) and (010) have the shortest reciprocal lattic

[Armani]

Can anyone explain why the two planes (100) and (010) in the HCP structure have the shortest reciprocal lattice vectors?
I mean it says {001}, but why is (001) not included?

 

[M Quack]

In the HCP structure you stack alternating layers in a ABAB... sequence. The (001) d-spacing is the distance between two A layers, and that is larger than the (100) d-spacing which is simply the diameter of the (hypothetical) spheres you stack.