Explanation​:
Strontium is in group 2 and so forms Sr2+ ions. The formula of the sulfide ion is S2− as sulfur is in group 16. For the positive and negative charges to cancel out, one of each ion is required.

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:​

Lithium is in group 1 and so forms Li+ ions. The formula of the nitride ion is N3−as nitrogen is in group 15. For the positive and negative charges to cancel out, three Li+ ions are needed for each N3− ion.

Explanation:​
Recall of description of metallic bonding as positive ions surrounded by delocalized electrons.

Explanation​:
Oxidation reaction; Magnesium is much less electronegative than oxygen, so the Mg atoms lose electrons to the O atoms during the reaction. This process forms positive Mg2+ ions, termed cations, and negative O2− ions, termed anions.

This question is categorized as easy, as the student must recall two pieces of information that are covered extensively in the syllabus.

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

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​:
Carboxylic acids have hydrogen bonding due to O−H bonds.

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​:
N2 has a triple bond, O2​ has a double bond, and H2only has a single bond.
The greater the number of shared pairs of electrons, the stronger the bond.

Explanation:​
Graphite is made up of individual graphene layers. Both have carbon atoms with three electron domains and trigonal planar shapes. Each carbon atom in diamond has four electron domains resulting in tetrahedral arrangements.

Explanation​:
The other three in theory, can form hydrogen bonds due to O−H and F−H bonds present.

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​:
All statements are correct, but only D is a reason for solubility in water

Explanation:​
Across the same period, metals have lower ionization energies than non-metals due to lower nuclear charges with the same number of shells (shielding effect).

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.

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​:
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:​
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​:
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:​
Alloys are homogeneous mixtures of metals with other metals or nonmetals.