Concept:Lithium exhibits anomalous behavior compared to the rest of the alkali metals. Because of its extremely high charge density, it can react directly with diatomic gases that are usually inert at room temperature.
Solution:- Air is primarily composed of Nitrogen (\( \approx 78\% \)) and Oxygen (\( \approx 21\% \)).
- When Lithium burns in air, it reacts directly with Oxygen to form a normal oxide:
$$ 4\text{Li} + \text{O}_2 \longrightarrow 2\text{Li}_2\text{O} $$
- Uniquely among the alkali metals, Lithium has a high enough lattice energy to break the strong triple bond of Nitrogen gas, forming Lithium nitride:
$$ 6\text{Li} + \text{N}_2 \longrightarrow 2\text{Li}_3\text{N} $$
- Therefore, it forms both the oxide and the nitride.
Why other options are incorrect:- Options A and B are incomplete on their own. Option C suggests peroxide/carbonate formation, but Lithium primarily forms the normal oxide, not a peroxide.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.