Among the following compounds, which one contains predominantly ionic bonds between its atoms?

Introduction / Context:
Chemical bonds can be broadly classified as ionic or covalent. Ionic bonds form when electrons are transferred from a metal atom to a non metal atom, creating oppositely charged ions that attract each other. Covalent bonds form when atoms share electron pairs. This question asks which of the listed compounds contains ionic bonding, a basic topic in general chemistry used to understand properties such as melting point and electrical conductivity.

Given Data / Assumptions:

• Ca is calcium, a metal, and O is oxygen, a non metal.
• C and N are non metals, and O is also a non metal.
• CO2, NO2, and NO are molecular compounds of non metals.
• We apply the general rule that metal plus non metal tends to form an ionic compound.

Concept / Approach:
In ionic compounds, metals lose electrons to form positive ions, and non metals gain electrons to form negative ions. For example, calcium loses two electrons to form Ca2+, while oxygen gains two electrons to form O2-, giving CaO as an ionic lattice. When only non metals are present, such as in CO2, NO2, and NO, the atoms usually share electrons, forming covalent bonds. Thus we need to identify the compound that is made from a metal and a non metal, which is CaO, calcium oxide.

Step-by-Step Solution:
Step 1: Analyse CaO. Ca is a metal and O is a non metal. Calcium loses electrons, oxygen gains electrons, forming Ca2+ and O2- ions. Step 2: Analyse CO2. C and O are both non metals; CO2 is a covalent molecular compound with double bonds. Step 3: Analyse NO2 and NO. N and O are both non metals, so NO2 and NO are covalent molecular compounds. Step 4: Select the compound with metal plus non metal. Only CaO fits the pattern of an ionic compound.

Verification / Alternative check:
Physical properties support this classification. Calcium oxide is a high melting, solid ionic compound that conducts electricity when molten, typical of ionic lattices. Carbon dioxide, nitrogen dioxide, and nitric oxide are gases at room temperature and do not form ionic crystals; they behave like molecular substances. Their bonding is explained by shared electron pairs rather than full electron transfer, which confirms that CaO is the only ionic compound in the list.

Why Other Options Are Wrong:
Option B: CO2 has covalent C=O bonds and is a typical molecular compound of non metals. Option C: NO2 is also covalent, with nitrogen and oxygen sharing electrons and existing as gas under normal conditions. Option D: NO is a diatomic molecule with covalent bonding between nitrogen and oxygen.

Common Pitfalls:
Students sometimes misclassify compounds because they see oxygen and assume ionic bonding, but the key is whether a metal is present. Others confuse properties of metal oxides, some of which may be covalent if the metal is very non metallic in nature. A simple rule at this level is that compounds of a metal with a typical non metal, like CaO or NaCl, are ionic, while compounds formed only from non metals tend to be covalent.

Final Answer:
The compound that contains ionic bonds is CaO, calcium oxide.