Which of the following values of heat of formation indicates that the product is the least stable?

Options

A. `-94` kcal
B. `-231.6` kcal
C. `+21.4` kcal
D. `+64.8` kcal

Answer

To determine which value of heat of formation indicates that the product is the least stable, we need to analyze the given options based on the concept of heat of formation (ΔH_f). The heat of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

### Step-by-Step Solution:

1. **Understanding Heat of Formation**:
- A negative value of heat of formation (ΔH_f < 0) indicates that the formation of the compound is exothermic, suggesting that the product is more stable.
- A positive value of heat of formation (ΔH_f > 0) indicates that the formation of the compound is endothermic, suggesting that the product is less stable.

2. **Analyzing the Options**:
- **Option 1: -94 kcal**: This is a negative value, indicating stability.
- **Option 2: -231.6 kcal**: This is also a negative value, indicating even greater stability than option 1.
- **Option 3: +21.4 kcal**: This is a positive value, indicating instability.
- **Option 4: -64.8 kcal**: This is a negative value, indicating stability.

3. **Identifying the Least Stable Product**:
- Among the options, the only positive value is from **Option 3 (+21.4 kcal)**. This indicates that the product is the least stable since it requires energy input for its formation.

### Conclusion:
The product corresponding to **Option 3 (+21.4 kcal)** is the least stable because it has a positive heat of formation.

---