Which of the following compounds has a negative enthalpy of solution?

Options

A. KCl
B. KBr
C. KF
D. KI

Answer

To determine which of the following compounds has a negative enthalpy of solution, we need to analyze the bond strengths of the compounds provided. The compounds in question are Kf (potassium fluoride), KCl (potassium chloride), KBr (potassium bromide), and KI (potassium iodide).

### Step-by-Step Solution:

1. **Understanding Enthalpy of Solution**:
- The enthalpy of solution is the heat change that occurs when a solute dissolves in a solvent. A negative enthalpy of solution indicates that the process is exothermic, meaning that energy is released when the solute dissolves.

2. **Bond Strength and Length**:
- The strength of ionic bonds decreases as the size of the ions increases. This is because larger ions have longer bond lengths, which results in weaker attractions between the ions.

3. **Analyzing the Compounds**:
- Kf (KF): Contains small ions (K+ and F-), which have strong ionic bonds.
- KCl (KCl): Contains K+ and Cl- ions. The bond is weaker than KF but still relatively strong.
- KBr (KBr): Contains K+ and Br- ions. The bond is weaker than KCl.
- KI (KI): Contains K+ and I- ions. The bond is the weakest among these compounds due to the larger size of I-.

4. **Conclusion**:
- As we move down the group from Kf to KI, the bond length increases and bond strength decreases. Therefore, KI will have the most negative enthalpy of solution because its ionic bonds are the weakest, allowing for easier dissolution and more energy release.

5. **Final Answer**:
- The compound with the most negative enthalpy of solution is **KI (potassium iodide)**.