Final answer:
The smallest bond angle is found in BeH₂, which is linear and has a bond angle of 180°.
Step-by-step explanation:
The molecule with the smallest bond angle between any two hydrogen atoms among the given options is BeH₂. This is because BeH₂ has a linear molecular geometry with a bond angle of 180°. In contrast, molecules such as CH₄, NH₃, and H₂O have bond angles of 109.5°, less than 109.5°, and approximately 104.5° respectively, due to their tetrahedral, trigonal pyramidal, and bent shapes caused by the presence of lone pairs of electrons which reduce the bond angles from the idealized tetrahedral angle.