Tar is a by-product of Wood, Petroleum, and Coal.

Wood:
- Tar can be produced from wood through a process called destructive distillation or pyrolysis.
- Destructive distillation involves heating wood in the absence of oxygen to break it down into various by-products, including tar.
- Tar obtained from wood is commonly known as wood tar or pine tar.

Petroleum:
- Tar can also be a by-product of petroleum refining processes.
- During the distillation of crude oil, various fractions are obtained, including gasoline, diesel, and kerosene.
- The residue left behind after the distillation process is known as petroleum tar or pitch.
- This tar is often used in road construction and waterproofing applications.

Coal:
- Coal tar is a by-product of coal gasification and coking processes.
- Coal gasification involves heating coal to produce a mixture of gases and other by-products, including coal tar.
- Coal tar can also be obtained during the coking process, where coal is heated in the absence of air to produce coke, gas, and coal tar.
- Coal tar has various industrial applications, including the production of chemicals, dyes, and pharmaceuticals.

Combination of Wood, Petroleum, and Coal:
- It is worth noting that the tar obtained from wood, petroleum, and coal may have different properties and applications.
- Wood tar is often used in traditional medicine, soap making, and as a wood preservative.
- Petroleum tar is commonly used in road construction and roofing materials.
- Coal tar, on the other hand, has a wide range of applications in the chemical industry.

Conclusion:
Tar is a versatile substance that can be produced from wood, petroleum, and coal. Each source of tar has its own unique properties and applications. Wood tar is obtained through the destructive distillation of wood, petroleum tar is a residue of petroleum refining processes, and coal tar is a by-product of coal gasification and coking. These tars find applications in various industries, including medicine, construction, and chemical manufacturing.