A mixture of KCl and KF is added to sodium chloride

Options

A. To increase the conductivity of NaCl
B. To decrease the melting point of NaCl
C. To suppress the degree of dissociation of NaCl
D. To decrease the volatility of NaCl

Explanation

To solve the question regarding the effect of adding a mixture of KCl and KF to sodium chloride (NaCl), we can follow these steps:

### Step 1: Understand the Concept of Impurities in Crystals
When impurities are added to a crystalline solid, they can disrupt the orderly arrangement of ions in the crystal lattice. This disruption can affect the physical properties of the solid, including its melting point.

**Hint:** Consider how the presence of different ions might affect the stability of the crystal lattice.

### Step 2: Identify the Components
In this case, we have:
- KCl (Potassium Chloride)
- KF (Potassium Fluoride)
- NaCl (Sodium Chloride)

Both KCl and KF contain potassium ions (K⁺), which can substitute for sodium ions (Na⁺) in the NaCl lattice.

**Hint:** Think about how the size and charge of the ions in KCl and KF compare to those in NaCl.

### Step 3: Analyze the Effect on Melting Point
The introduction of K⁺ ions from KCl and K⁺ ions from KF into the NaCl lattice will create a mixed ionic environment. This can lead to a distortion of the face-centered cubic (FCC) structure of NaCl.

As a result of this distortion, the ionic bonds in the NaCl lattice become weaker, making it easier for the lattice to break apart when heat is applied. Therefore, the melting point of NaCl will decrease.

**Hint:** Consider how the strength of ionic bonds is related to the melting point of a compound.

### Step 4: Conclusion
The addition of KCl and KF to NaCl will lower the melting point of NaCl due to the distortion of its crystal lattice caused by the presence of different ions.

**Final Answer:** The melting point of NaCl decreases when a mixture of KCl and KF is added.