What type of elements form interstitial hydrides ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Interstitial Hydrides**: Interstitial hydrides are compounds formed when hydrogen atoms occupy the interstitial spaces (the gaps) in the crystal lattice of metals.

2. **Identifying the Elements**: The elements that typically form interstitial hydrides are primarily found in the D and F blocks of the periodic table.

3. **Reason for Formation**: The D and F block elements have vacant N-1D orbitals. This allows them to accommodate small atoms like hydrogen, carbon, nitrogen, and boron in their crystal structure.

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