Steam coal is a type of coal that is commonly used to generate steam in power plants for the production of electricity. It is a key component in the energy industry and plays a crucial role in meeting the global demand for electricity.

The correct option for steam coal is 'D', which refers to non-coking bituminous coal. Let's explore why non-coking bituminous coal is the correct answer:

1. Types of Coal:
- There are four main types of coal: anthracite, bituminous, sub-bituminous, and lignite. These types are classified based on their carbon content, energy content, and geological origin.
- Steam coal falls under the category of bituminous coal, which is the most abundant and widely used type of coal.

2. Bituminous Coal:
- Bituminous coal is a dense and black coal that contains a high carbon content, typically ranging from 45% to 86%. It is formed from the remains of plants and trees that lived millions of years ago.
- This type of coal has a relatively high energy content and is commonly used for electricity generation, industrial processes, and as a fuel for steam locomotives.

3. Coking vs. Non-Coking Coal:
- Bituminous coal can be further classified into coking or non-coking coal based on its ability to produce coke, a solid carbonaceous residue used in the production of steel.
- Coking bituminous coal has the ability to undergo a process called coking, where it is heated in the absence of air to remove volatile components and produce coke.
- On the other hand, non-coking bituminous coal does not have the necessary properties to form coke and is primarily used as a fuel for power generation.

4. Steam Coal:
- Steam coal, also known as thermal coal, is primarily used for electricity generation through steam turbines. It is pulverized into a fine powder and burned in large boilers to produce high-pressure steam.
- The steam is then used to drive turbines connected to generators, which produce electricity.
- Non-coking bituminous coal is the preferred type of coal for steam generation due to its high energy content and availability.

In conclusion, steam coal refers to non-coking bituminous coal, which is widely used for electricity generation. It is important in meeting the global demand for electricity and plays a significant role in the energy industry.