Graphite and diamond are both allotropes of carbon, meaning they are different forms of the same element. While they have some similarities, there are also several key differences between them. The incorrect statement among the options given is option 'D' - "Physical and chemical properties of graphite and diamond are different."

1. Physical Properties:
- Graphite: Graphite has a layered structure consisting of parallel sheets of carbon atoms. Each carbon atom is bonded to three others in a trigonal planar arrangement, forming hexagonal rings. These sheets can slide over each other easily, giving graphite its smooth and slippery texture. Graphite is opaque and has a grey-black color.
- Diamond: Diamond has a three-dimensional crystal lattice structure where each carbon atom is bonded to four others in a tetrahedral arrangement. This results in a strong and rigid structure, making diamond extremely hard. Diamond is transparent and colorless, although impurities can give it various colors.

2. Electrical Conductivity:
- Graphite: Graphite is a good conductor of electricity. The delocalized electrons in the carbon layers can move freely, allowing electric current to pass through.
- Diamond: Diamond is an insulator and does not conduct electricity. The strong covalent bonds in the diamond structure hold the electrons tightly, preventing them from moving freely.

3. Thermal Conductivity:
- Graphite: Graphite is a good conductor of heat. The carbon layers in graphite are loosely packed, allowing heat to transfer easily through the material.
- Diamond: Diamond is an excellent conductor of heat. The rigid and closely-packed diamond structure allows heat to be conducted rapidly, making diamond one of the best thermal conductors.

4. Chemical Properties:
- Graphite: Graphite is chemically stable and does not react easily with most substances. It is resistant to acids, bases, and other chemicals.
- Diamond: Diamond is also chemically stable and highly resistant to chemical reactions. It is not easily affected by acids, bases, and other substances.

In summary, graphite and diamond have different physical and chemical properties. Graphite is smooth and slippery, a good conductor of electricity, and an average conductor of heat. On the other hand, diamond is extremely hard, transparent, a poor conductor of electricity, and an excellent conductor of heat.