Question

what best explains the difference in melting points between cl₂ (-101.5) and f₂ (-219)?
increased number of electrons in chlorine
increased mass (polarizability) of chlorine
increased electronegativity of fluorine
decrease metallic character of fluorine

Explanation:

Both \(Cl_2\) and \(F_2\) are non - polar molecules. The main intermolecular force between them is London dispersion forces. London dispersion forces increase with the number of electrons (or molecular mass, as more electrons are generally associated with a heavier molecule). Chlorine (\(Cl_2\)) has more electrons than fluorine (\(F_2\)). A higher number of electrons means stronger London dispersion forces. Stronger intermolecular forces require more energy to break, resulting in a higher melting point. Electronegativity affects bond polarity (not relevant here as both are non - polar). Metallic character is not relevant for these non - metallic diatomic molecules. While mass is related to the number of electrons (more electrons in \(Cl_2\) mean a higher mass), the root cause is the increased number of electrons leading to stronger London dispersion forces.

Answer:

Increased number of electrons in chlorine.