Answer: The three dimensional shape of H-Be-H molecule is Linear.
Explanation: Be is a second group metal with only two valence electrons and H has only one valence electron. H wants to complete two electrons in its valence shell and for this each H forms a single covalent bond with central Be atom. As only two atoms(H atoms) are bonded to central Be atom and it does not have any lone pair of electrons, it's Linear in shape. The bond angle is 180 degree.
If you see any molecule where only two atoms are bonded to the central atom and the central atom doesn't have any lone pair of electrons then it must be Linear in shape.