Interstitial hydrides are formed by d and f block elements.

Explanation:
- Interstitial hydrides are a class of compounds in which hydrogen atoms occupy the interstitial positions between the metal atoms in a solid lattice.
- These hydrides are typically formed by elements from the d and f block of the periodic table.
- The d block elements, also known as transition metals, have partially filled d orbitals which allow for the formation of interstitial hydrides.
- Transition metals such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, and platinum are known to form interstitial hydrides.
- The f block elements, also known as inner transition metals, have partially filled f orbitals which also facilitate the formation of interstitial hydrides.
- Elements from the lanthanide and actinide series, such as cerium, neodymium, samarium, uranium, and plutonium, can form interstitial hydrides.
- These elements have a high affinity for hydrogen and can accommodate hydrogen atoms in the interstitial sites within their crystal lattice.
- The formation of interstitial hydrides is often associated with the ability of these elements to undergo significant changes in their electronic structure upon hydrogen absorption.
- The hydrogen atoms occupy the interstitial positions between the metal atoms, leading to the expansion of the lattice and changes in the physical and chemical properties of the material.
- Interstitial hydrides often exhibit unique properties such as high hydrogen storage capacity, thermal stability, and catalytic activity.
- These properties make them useful in various applications such as hydrogen storage materials, catalysts, and hydrogen purification systems.
- In conclusion, interstitial hydrides are primarily formed by elements from the d and f block of the periodic table, as these elements have the necessary electronic structure to accommodate hydrogen atoms in the interstitial positions.