Explanation:
Fluorine is the most electronegative element on the periodic table. Therefore, the greatest difference in electronegativity between $\mathrm{C}$ and $\mathrm{F}$ results in the most polar bond.

Explanation​:
Volatility refers to the ease at which a substance vaporizes. Ionic bonds are very strong and, therefore, a lot of energy is required to turn ionic compounds into gases.

Polar solvents are able to form electrostatic forces of attraction with ions.

Explanation:​
Metals characteristically have high melting points due to strong metallic bonds.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2CaX3​NX2​ is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation​:
There is no polyatomic ion with the formula of CO4 ^2−​. The correct formula for the carbonate ion is CO3^2−​. The formulas and charges of the other ions are correct.

Explanation​:
Metals and non-metals have the greatest differences in electronegativity and so ionic bonds are formed.

Explanation​:
Choice A refers to ionic bonding;
Choice B could refer to ionic bonding or specifically coordinate (dative) bonding;
Choice C refers to hydrogen bonding.

Explanation:​
SiO2​ has a giant covalent structure where each Si atom is singly bonded to four oxygen atoms (while maintaining a Si

ratio of 1:2).
As there are four electron domains around each silicon atom, the structure has a tetrahedral arrangement. SiO2​ is held together by strong covalent bonds requiring a large amount of energy to overcome, resulting in a high melting point.
The strong bonds, together with the fact that there are no charged particles present, lead to insolubility in polar solvents such as water.

Explanation:​
Atom 1 has four electron domains and so a tetrahedral shape (109.5$°$).
Atom 2 has three electron domains and so a trigonal planar shape (120$°$).
Atom 3 has four electron domains of which one is a lone pair giving it a trigonal pyramidal shape (107$°$).

Explanation​:
Neither material is electrically conductive. Diamond has no delocalized electrons, while the delocalized electrons in buckminsterfullerene are confined within the molecule. There is no extended lattice of bonds through which the electrons can move in response to an applied potential difference. Diamond is a hard material; a large force is required to break the strong covalent bonds between atoms.

Buckminsterfullerene, however, is soft, as only a small force is needed to overcome the weak intermolecular (London / dispersion) forces between molecules.

This question is moderately difficult, as the student must recall multiple features of the two carbon allotropes or deduce their physical properties from the diagrams given.

Explanation​:
There is no polyatomic ion with the formula of CO42−COX42−​. The correct formula for the carbonate ion is CO32−COX32−​. The formulas and charges of the other ions are correct.

Explanation​:
There is no polyatomic ion with the formula of CO42−COX42−​. The correct formula for the carbonate ion is CO32−COX32−​. The formulas and charges of the other ions are correct.

Explanation​:
Simple molecular covalent structures cannot conduct electricity due to an absence of charged particles. $\mathrm{NaCl}$ is an ionic compound that has ions that are free to move when in a molten state.

Explanation​:
There is no polyatomic ion with the formula of CO42−COX42−​. The correct formula for the carbonate ion is CO32−COX32−​. The formulas and charges of the other ions are correct.

Explanation:​
To answer this question, the student must apply the data to the van Arkel-Ketelaar triangle to determine the type of bonding present in the molecule.

The bonding triangle analysis shows that the material is an ionic compound. Therefore, characteristic properties include that it is a crystalline lattice with a high melting point.

This question is categorized as easy since the student only needs to apply the data to Section 17 of the data booklet and then recall the basic properties of matter.

Explanation:​
The strength of metallic bonding and therefore melting point, decreases down a group due to increasing atomic radius (more energy levels) and greater separation of the nuclei. Cs is in period 6, while all other 3 elements are in period 5. Hence, Cs has the lowest melting point. Since atomic radius decreases across a period due to increased effective nuclear charge, the strength of metallic bonding, and therefore melting point, increases from Rb to Zr.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2​ is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2​ is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:​
Electrostatic forces of attraction between the positive ions and delocalized electrons (metallic bonds) must be broken for metal to melt. The stronger the metallic bond, the higher the melting point.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2​ is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation​:
2-methylpentane is branched and therefore has a lower surface area. The lower the surface area, the weaker the London (dispersion) forces and the lower the boiling point.

Explanation:
The higher the charge of the ions, the stronger the electrostatic forces of attraction and, therefore, the greater the lattice enthalpy.
The smaller the ion, the greater the charge density and the stronger the electrostatic attraction between oppositely charged ions.
Statement I is incorrect since the smaller the lattice enthalpy, the weaker the electrostatic attraction and the lower the melting point is.