Highest Melting Point: BeCl2

Explanation:

Introduction:
Melting point is the temperature at which a solid substance undergoes a phase change and transforms into a liquid state. It is an important property of a substance that helps determine its physical characteristics. In the given options, the substance with the highest melting point is BeCl2, i.e., Beryllium chloride.

Factors Affecting Melting Point:
The melting point of a substance depends on various factors, including intermolecular forces, molecular weight, and crystal structure. The strength of intermolecular forces determines the amount of energy required to break the bonds and transition from solid to liquid state.

Intermolecular Forces:
Intermolecular forces are attractive forces between molecules. The types of intermolecular forces include London dispersion forces, dipole-dipole forces, and hydrogen bonding. Stronger intermolecular forces result in higher melting points.

Comparison of AlCl3, LiCl3, NaCl, and BeCl2:
To determine the substance with the highest melting point, let's compare the intermolecular forces and other factors for each option:

1. AlCl3 (Aluminum chloride):
- Aluminum chloride exists as a covalent compound with ionic character.
- It forms ionic bonds due to the electronegativity difference between aluminum and chlorine.
- The compound has a high melting point but lower than BeCl2.

2. LiCl3 (Lithium chloride):
- Lithium chloride is an ionic compound with strong ionic bonds.
- It has a relatively high melting point due to the strong electrostatic attractions between lithium and chloride ions.
- However, its melting point is lower than BeCl2.

3. NaCl (Sodium chloride):
- Sodium chloride is also an ionic compound with a regular crystal lattice structure.
- It has a high melting point due to the strong ionic bonds between sodium and chloride ions.
- However, its melting point is lower than BeCl2.

4. BeCl2 (Beryllium chloride):
- Beryllium chloride is a covalent compound.
- It has a unique crystal structure with covalent bonds between beryllium and chloride atoms.
- The covalent nature of BeCl2 results in stronger intermolecular forces and a higher melting point compared to the other options.

Conclusion:
Among the given options, BeCl2 (Beryllium chloride) has the highest melting point. Its covalent nature and unique crystal structure contribute to stronger intermolecular forces, requiring higher energy for the transition from solid to liquid state.

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