Question

The correct order of melting points of the following salts is: 
LiCl & (I) 
LiF & (II) 
LiBr & (III) 
 

• A. \(I>II>III\)
• B. \(II>I>III\)
• C. \(III>II>I\)
• D. \(II>III>I\)

Hint:

The melting point of ionic compounds decreases as the anion size increases because larger anions lead to weaker lattice energy.

Answer 1

The Correct Option is B

Step 1: Understanding Melting Point Trends in Ionic Compounds 
The melting point of an ionic compound depends on: 1. Lattice Energy: Higher lattice energy means a higher melting point. 2. Size of the Anion: Smaller anions lead to stronger lattice energy. 
Step 2: Analyzing the Given Salts 
Fluoride (F$^-$) is the smallest anion, followed by chloride (Cl$^-$) and bromide (Br$^-$). 
The order of lattice energy is: \[ LiF>LiCl>LiBr \] Since lattice energy determines melting point, we get: \[ LiF>LiCl>LiBr \] 
Step 3: Correct Answer 
Thus, the correct order is: \[ {\(LiF (II)>LiCl (I)>LiBr (III)\)} \] Thus, the correct answer is (B).

Answer 2

Step 1: Identify the compounds
The salts given are lithium halides:
I. LiCl (Lithium chloride)
II. LiF (Lithium fluoride)
III. LiBr (Lithium bromide)

Step 2: Understand factors affecting melting point
The melting point of ionic compounds depends on:
- Lattice energy (the energy required to separate one mole of the solid into gaseous ions)
- The charges on ions (same for all here: Li⁺ and halide⁻)
- The size of the ions (smaller ions = stronger electrostatic attraction = higher lattice energy)

Step 3: Compare the halide ions
- F⁻ is the smallest halide ion
- Cl⁻ is larger than F⁻
- Br⁻ is even larger than Cl⁻
As the size of the halide ion increases, the lattice energy decreases, and thus the melting point also decreases.

Step 4: Arrange the compounds by melting point
- LiF: highest lattice energy → highest melting point
- LiCl: intermediate lattice energy → moderate melting point
- LiBr: lowest lattice energy → lowest melting point

Step 5: Final order
LiF (II) > LiCl (I) > LiBr (III)

Final Answer: \( II > I > III \)