Final answer:
Beryllium chloride (BeCl₂) has a high melting point due to its giant ionic structure with strong ionic bonds, while boron trichloride (BCl₃) has low melting and boiling points because of its simple molecular structure with weak intermolecular forces.
Step-by-step explanation:
Beryllium chloride (BeCl₂) and boron trichloride (BCl₃) have different melting and boiling points due to the type of bonds and molecular structures they possess. BeCl₂ has a giant ionic structure, which means it is formed by a lattice of positively and negatively charged ions held together by strong ionic bonds. This ionic bond formation in BeCl₂ requires a significant amount of energy to break, resulting in a high melting point.
On the other hand, BCl₃ has a simple molecular structure with trigonal planar geometry, which means it has covalent bonds that share electrons between the boron and chlorine atoms. However, the intermolecular forces between BCl₃ molecules are much weaker van der Waals forces (dispersion forces), and therefore, BCl₃ has relatively low melting and boiling points.
To summarize, the correct answer to the question is (c) Beryllium chloride has a giant ionic structure; boron trichloride has a simple molecular structure.