For which of the following substance(s), the standard enthalpy of formation is/are zero? — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Standard enthalpy of formation is exactly zero for elements strictly in their most stable reference state at standard conditions. For carbon, it's graphite; for bromine, it's liquid $\text{Br}_2$. Ozone and iodine gas are not standard reference states.