Lanthanoids (Ln) when heated with nitrogen, form compounds of the type _____.

$LnN$

The correct answer is Option (3) → $LnN$

Lanthanoids (Ln, atomic numbers 58–71) are highly electropositive and reactive metals. When heated with nitrogen (typically at high temperatures), they form nitrides with the formula LnN (lanthanoid(III) nitride).

• Most lanthanoids exhibit a stable +3 oxidation state.
• The reaction is: 2Ln + N₂ → 2LnN
• These nitrides are ionic compounds with Ln³⁺ and N³⁻ ions.

Examples:

• Cerium nitride: CeN
• Lanthanum nitride: LaN
• Praseodymium nitride: PrN

Why not the others?

• Ln₂N: Would imply +1 oxidation state (unstable for lanthanoids).
• LnN₂: Would imply +4 oxidation state (rare, not typical with N₂).
• Ln₂N₃: Would imply +3 state but incorrect stoichiometry (should be 2Ln : 3N → but actual is 1:1).