<span>Answer: B. Ionic solids have higher melting points than molecular solids.
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This is because the rest are false, as solids are able to melt, and do have melting points. Also, not all solids have the same melting points.
Sulfur will float, and iron will sink because each will retain its properties.
“Iron will float, and sulfur will sink because each will lose its properties” is <em>incorrect</em>. A substance will lose its properties only if it reacts to form a new substance.
“Both will float because they are physically mixed” is <em>incorrect</em>. The substances in a mixture retain their properties.
“Both will float because they react chemically” is <em>incorrect</em>. Iron and sulfur do not react at room temperature. Even if they did, the iron sulfide would sink.
Explanation:
Van der Waals interactions occur between any two or more molecules. They are caused by a fluctuation in electron density, as electrons are not actually fixed in a shell, but actually freely moving as a 'cloud of electron density'. This means that sometimes one end of a molecule can become more partially negatively charged as all electrons move to that side, and conversely it can attract the more partially positive end of a molecule (that has little electrons).
Hydrogen bonds only occur between molecules that contain oxygen, nitrogen and fluorine bonded to a hydrogen atom.
Hydrogen bonding is also the strongest intermolecular force there is, but not strong in comparison to ionic and covalent bonds. Therefore, hydrogen bonds are much stronger than Van der Waals forces. Hydrogen bonds only form if oxygen, nitrogen and fluorine are bonded to a hydrogen atom, as they have the greatest electronegativity differences (look at an electronegativity table), and when the overall molecule is polar (have unequal charges). This allows the molecule to be able to attract another molecule from one of the bonded atoms to a hydrogen atom.
