When do non-polar covalent bonds typically occur?

Non-polar covalent bonds typically occur when atoms share electrons equally due to having similar electronegativities. This equal sharing happens primarily between identical atoms or atoms that are very close in electronegativity. For example, diatomic molecules like N₂, O₂, and Cl₂ form non-polar covalent bonds due to the identical nature of the atoms involved.

In relation to the choices, the occurrence of non-polar covalent bonds does not depend specifically on the crystalline form of a substance. While some non-polar molecules can indeed form crystalline structures under certain conditions, this is not a defining characteristic of non-polar covalent bonding itself. Instead, such bonds are characterized by their lack of polarity rather than their physical state.

In contrast, polar covalent bonds and ionic bonds display properties that depend heavily on electronegative differences and solubility in polar solvents like water. Non-polar molecules, on the other hand, generally do not conduct electricity well, which aligns with the low tendency for electrical conductivity mentioned in the correct answer. Thus, a more nuanced understanding of bond formation will show that while non-polar molecules can exist in various states, their defining characteristic lies in the nature of electron sharing rather than the solid or crystalline