Final answer:
The reaction in option D represents the formation of one mole of nickel(II) oxide from its elements in their standard states, making its enthalpy the same as the enthalpy of formation.
Step-by-step explanation:
The question is asking for the enthalpy of formation, which is the heat change that results when one mole of a compound is formed from its elements in their standard states. For the enthalpy of the reaction to be the same as the enthalpy of formation, the reaction must represent the formation of one mole of a compound from its elements in their standard states. The answer to the question, "For which one of the following is the enthalpy of the reaction the same as the enthalpy of formation?", is D) Ni (s) + ½ O₂ (g) → NiO (s). This reaction shows the formation of one mole of nickel(II) oxide (NiO) from its constituent elements, nickel (in the solid state) and oxygen (in the gaseous state).
A formation reaction is typically represented by its elements in their most stable form at 1 atmosphere of pressure and 25 degrees Celsius (298 K) transitioning to form one mole of the compound in its standard state. This definition aligns with the reaction provided in option D. This is an example of a basic concept within thermochemistry which utilizes Hess's Law to calculate enthalpy changes of reactions given the enthalpies of formation for reactants and products.