The correct answer is option 'B', which refers to the reciprocating engine. Let's understand why the reciprocating engine is the correct choice when it comes to petrol and diesel engines in the automobile industry.

Reciprocating Engine:
A reciprocating engine is a type of internal combustion engine that converts the chemical energy of fuel into mechanical energy by utilizing reciprocating linear motion. It is the most common type of engine used in automobiles today. This engine consists of a cylinder, piston, and crankshaft.

Key Points:
1. Internal Combustion Engine: Reciprocating engines are a type of internal combustion engine, which means that the fuel combustion occurs internally within the engine itself.

2. Fuel Conversion: The reciprocating engine converts the chemical energy of fuel (petrol or diesel) into mechanical energy. This conversion takes place through a four-stroke cycle: intake, compression, combustion, and exhaust.

3. Working Principle: The reciprocating engine works on the principle of reciprocating motion. The piston moves up and down within the cylinder, driven by the combustion of fuel. This motion is transferred to the crankshaft, which converts it into rotational motion.

4. Fuel Types: Reciprocating engines can run on both petrol and diesel fuels. Petrol engines use spark ignition, while diesel engines use compression ignition.

5. Applications: Reciprocating engines are widely used in automobiles, including cars, motorcycles, trucks, and buses. They are also used in other applications such as generators, aircraft, and small boats.

6. Advantages: Reciprocating engines offer several advantages, including high power-to-weight ratio, compact size, easy maintenance, and widespread availability of fuels.

7. Disadvantages: On the downside, reciprocating engines can be less fuel-efficient compared to other engine types, such as rotary engines. They also produce more vibrations and noise.

In conclusion, the correct answer is option 'B', the reciprocating engine, when it comes to petrol and diesel engines used in the automobile industry. Reciprocating engines are widely used, offer good power-to-weight ratio, and can run on both petrol and diesel fuels.