In basic chemical bonding, which of the following molecules contains a purely non polar covalent bond in which the bonding electrons are shared equally between identical atoms?

Introduction / Context:
This question tests the idea of non polar covalent bonding in basic chemistry. In a non polar covalent bond, the bonding electrons are shared equally between the atoms. This usually happens when the two atoms have the same or very similar electronegativities. Understanding this concept helps learners distinguish between polar bonds, non polar bonds, and non polar molecules, which is important for predicting physical properties such as solubility and boiling point.

Given Data / Assumptions:

• We are given several molecules: Br2, CO, CO2, CCl4, and H2O.
• We are asked which molecule contains a non polar covalent bond.
• Assume standard electronegativity values from the periodic table.
• Assume bonds are single or multiple covalent bonds between the atoms shown in the formula.

Concept / Approach:
The key concept is electronegativity difference. When two atoms have the same electronegativity, the electrons are shared equally and the bond is non polar covalent. When the electronegativity difference is significant, the bond becomes polar covalent. In diatomic molecules of the same element, such as Br2, the bond is always non polar because both atoms attract electrons equally. In heteronuclear molecules like CO, CO2, CCl4, and H2O, the bonds are generally polar because the atoms have different electronegativities.

Step-by-Step Solution:

Verification / Alternative check:
An alternative way to check is to remember the simple rule that any molecule formed from two atoms of the same element, such as H2, N2, O2, F2, Cl2, Br2, and I2, will always contain a non polar covalent bond. All the other molecules listed are formed from different elements, so their bonds are polar. This confirms that Br2 is the only correct choice.

Why Other Options Are Wrong:

• CO: The C–O bond is polar covalent due to a large difference in electronegativity between carbon and oxygen.
• CO2: Each C–O bond is polar covalent, even though the entire molecule can be non polar in shape.
• CCl4: Each C–Cl bond is polar covalent; the molecule is symmetric but the individual bonds are not non polar.
• H2O: The O–H bonds are polar covalent, which is why water is a highly polar molecule.

Common Pitfalls:
Students sometimes confuse a non polar molecule with a non polar bond. A molecule like CO2 or CCl4 can be overall non polar because of molecular geometry, even though the individual bonds are polar. In this question the focus is specifically on the non polar covalent bond itself, not the net polarity of the whole molecule. Forgetting to make this distinction is a frequent source of mistakes in introductory chemistry questions.

Final Answer:
The molecule that contains a purely non polar covalent bond is Br2.