Which of the following metal hydrides has the crystal structure of rutile? 

CONCEPT:

Rutile Crystal Structure

• The rutile crystal structure is a tetragonal structure commonly observed in compounds like titanium dioxide (TiO₂).
• This structure consists of metal cations (e.g., Ti⁴⁺ in TiO₂) surrounded by oxygen anions (or hydride ions in metal hydrides) in a specific arrangement.
• The coordination number of the metal cation in the rutile structure is 6, meaning it is surrounded by 6 anions in an octahedral geometry.

EXPLANATION:

Rutile structure

MgH₂

• MgH₂ has the rutile crystal structure. This is because:
  • Magnesium (Mg²⁺) forms a coordination number of 6 with hydride ions (H^-).
  • This results in a tetragonal rutile-like arrangement, similar to TiO₂ but with H^- ions replacing O^2-.
• Other compounds:
  • LiH and NaH crystallize in a rock salt structure (not rutile).
  • BaH₂ adopts an orthorhombic structure (not rutile).

Therefore, the correct answer is Option 1: MgH₂.