Question

Identify the correct decreasing order of lattice enthalpy for metal fluorides from following.

• A. \(\text{KF}>\text{NaF}>\text{LiF}\)
• B. \(\text{NaF}>\text{KF}>\text{LiF}\)
• C. \(\text{LiF}>\text{KF}>\text{NaF}\)
• D. \(\text{LiF}>\text{NaF}>\text{KF}\)

Hint:

With the same charges and the same anion, lattice enthalpy rises as the cation gets smaller.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
Lattice enthalpy is proportional to \(\dfrac{q_1q_2}{r_1+r_2}\). A smaller interionic distance gives a larger lattice enthalpy.

Step 2: Compare the ions
In LiF, NaF and KF the charges are the same and the anion \(\text{F}^{-}\) is the same. Only the cation size differs.

Step 3: Order
The cation size increases as \(\text{Li}^{+}<\text{Na}^{+}<\text{K}^{+}\), so lattice enthalpy decreases in the order LiF > NaF > KF.

Final Answer:
The decreasing order is LiF > NaF > KF. \[ \boxed{\text{(D) }\text{LiF}>\text{NaF}>\text{KF}} \]