The heat of formation is the change in enthalpy accompanying the formation of a substance fiom its elements at 298 K and 1 atm pressure. Since the anthalpies of elements are taken to be zero, the heat of formation `(triangleH)` of compounds

Answer

To solve the question regarding the heat of formation (ΔH) of compounds, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Heat of Formation**: The heat of formation (ΔH) is defined as the change in enthalpy when one mole of a substance is formed from its elements in their standard states (1 atm pressure and 298 K).

2. **Enthalpy of Elements**: It is important to note that the enthalpy of elements in their standard states is defined to be zero. This means that when we calculate the heat of formation for a compound, we are looking at the change in enthalpy from this zero point.

3. **Heat of Formation of Compounds**: The heat of formation of a compound can either absorb energy (endothermic reaction) or release energy (exothermic reaction). Therefore, the ΔH for the formation of a compound can be either positive or negative.

4. **Conclusion**: Since the heat of formation depends on the nature of the compound being formed and the reaction involved, it can be concluded that the heat of formation (ΔH) of compounds may be negative or positive.

5. **Final Answer**: The correct option is that the heat of formation may be negative or positive.