Final answer:
The heat of formation is equal to zero for an element in its most stable form at 25°C and 1 atm. For the provided options, F₂ is the correct one, as it is in its diatomic molecular form, which is its standard state, and thus has a standard heat of formation of zero, the correct option is D).
Step-by-step explanation:
The question asks which of the given options has a heat of formation equaling zero. By definition, the standard enthalpy of formation (ΔH°f) of any element in its most stable form is zero at 25°C and 1 atm. The elements in their standard states, which are diatomic molecules for some gases, have a standard heat of formation of zero.
Considering the provided options, H denotes atomic hydrogen, which is not in its standard state because the standard state is diatomic hydrogen (H₂).
N stands for atomic nitrogen, which is not in its standard state either, because the standard state for nitrogen is diatomic nitrogen (N₂). O for oxygen is similar; its standard state is diatomic oxygen (O₂). Therefore, A) H, B) N, and C) O do not have a heat of formation of zero because they are not in their diatomic standard state forms.
F₂, however, is in its standard state. It is a diatomic molecule at 25°C and 1 atm, making it the most stable form of fluorine under these conditions. Thus, the heat of formation for F₂ is zero. Option D) F₂ is the correct answer.