NDA General Ability Question (2026) — Solution

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Graphite is the thermodynamically most stable allotrope of carbon at standard temperature and pressure. The standard enthalpy of formation, _ f H^ , for graphite is taken as zero. Other allotropes such as diamond and fullerene have positive standard enthalpies of formation, indicating they are less stable than graphite. Coal is an amorphous form of carbon and is also less stable than graphite. Answer: Graphite