Concept: The question asks to identify the incorrect characteristic of a $\pi$-bond. Understanding the formation and properties of $\pi$-bonds is crucial.

Why (B) is incorrect:

A $\pi$-bond is formed by the lateral (sideways) overlap of unhybridized p-orbitals. Hybrid orbitals are primarily involved in forming $\sigma$-bonds and determining molecular geometry. Therefore, the statement that $\pi$-bonds are formed from hybrid orbitals is incorrect.

Option Analysis:

• A) $\pi$ - bond is usually formed when a sigma bond is already formed. This is correct. In multiple bonds (double or triple bonds), one bond is always a $\sigma$-bond, and the subsequent bonds are $\pi$-bonds. The $\sigma$-bond provides the primary linkage between atoms.
• B) $\pi$ - bond is formed from hybrid orbitals. This is incorrect. $\pi$-bonds are formed by the lateral overlap of unhybridized p-orbitals. Hybrid orbitals form $\sigma$-bonds.
• C) $\pi$ - bond may be formed by the overlapping of p-orbitals. This is correct. Specifically, it's the lateral overlap of unhybridized p-orbitals that forms $\pi$-bonds.
• D) $\pi$-bond results from lateral overlap of atomic orbitals. This is correct. Lateral or sideways overlap of atomic orbitals (typically p-orbitals) leads to the formation of a $\pi$-bond, where the electron density is above and below the internuclear axis.

Correct Answer: (B)