Aromatic hydrocarbons are a specific type of hydrocarbon that possess a unique structure called an aromatic ring. This ring is formed by a series of alternating double and single bonds, and it is highly stable and planar in shape. Aromatic hydrocarbons are known for their distinctive smells and are commonly found in many organic compounds, including benzene.

The correct statement related to aromatic hydrocarbons is option 'D' - they have a sigma and delocalized pi bond.

Explanation:

Sigma Bond:
- A sigma bond is a type of covalent bond formed by the overlap of atomic orbitals along the bond axis.
- In the case of aromatic hydrocarbons, each carbon atom in the aromatic ring is bonded to three other atoms, either carbon or hydrogen.
- These bonds are formed by the overlap of the sp2 hybridized orbitals of carbon atoms, resulting in the formation of sigma bonds.

Pi Bond:
- A pi bond is a type of covalent bond formed by the overlap of adjacent p orbitals that are oriented perpendicular to the bond axis.
- In the case of aromatic hydrocarbons, the alternating double bonds in the aromatic ring are formed by the overlap of p orbitals.
- Each double bond consists of one sigma bond and one pi bond.
- The pi bond is formed by the sideways overlap of p orbitals above and below the plane of the ring.
- This pi bond is delocalized, meaning that it is not localized between two specific carbon atoms but rather spread over the entire ring.

Sigma and Delocalized Pi Bond:
- Aromatic hydrocarbons have both sigma and delocalized pi bonds.
- The sigma bonds are formed between adjacent carbon atoms in the ring, while the delocalized pi bond is spread over the entire ring.
- The delocalization of the pi bond in the aromatic ring contributes to the high stability of aromatic compounds.
- This delocalization allows for the distribution of electron density throughout the ring, making it highly resistant to reactions that would break the aromaticity.

In conclusion, aromatic hydrocarbons have both sigma and delocalized pi bonds. The sigma bonds are formed by the overlap of sp2 hybridized orbitals of carbon atoms, while the delocalized pi bond is formed by the sideways overlap of p orbitals and is spread over the entire ring. This unique bonding arrangement gives aromatic hydrocarbons their stability and distinctive properties.