Explanation:​
The central atom is carbon with two C-H single bonds and one C=O bond. This gives 3 electron domains and 8 valence electrons.

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

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

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

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:​
C3H6​ belongs to the alkene class with the general formula CnH2n​, and has a three carbon chain.

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

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​:
Recall that hydrogen bonds are the strongest intermolecular forces, and London forces are the weakest.

Explanation:
Oppositely charged ions attract, it is an ionic bonding;

Choice A describes metallic bonding;

Choice B describes a simple molecular lattice;

Choice D describes a covalent bond.

Explanation:
Ionic bonds form between oppositely charged ions; NH4^+ and SO4^2− in ammonium sulfate and Na^+ and CO3^2− in sodium carbonate.

Due to a smaller difference in electronegativity and both being nonmetals, $\mathrm{l}$ bonds are polar covalent.

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​:
Magnesium has two electrons in its outermost shell and loses both to achieve a full outer shell (Mg^2+). Fluorine has seven electrons in its outermost shell; it needs one more electron to achieve a full outer shell (F^1−).

Two fluorine atoms are therefore required for each magnesium atom in order to form a neutral ionic compound (where the charges of the positive and negative ions cancel out).

Explanation​:
NH3​ has all of the bonds/forces named above, but its high boiling point is due to the presence of hydrogen bonds which are the strongest intermolecular forces. Hydrogen bonding is possible due to the presence of N−H bonds.

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

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:
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:​
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​:
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:​
In SO2​, the sulfur is bound to two oxygen atoms.
The central sulfur has one non-bonding pair of electrons giving it three electron domains in total.
CS2​, BeCl2​, and C2​H2​ have two electron domains on their central atoms and have linear shapes.