Volcanic soils are soils in which more than half of the parent mineral matter is volcanic ash and appear very dark in color. They are formed from the weathering and decomposition of volcanic rock and ash, which are rich in nutrients and minerals. Here is a detailed explanation of why the correct answer is option 'B' - Volcanic soil.

Heading: Characteristics of Volcanic Soil

- Dark Color: Volcanic soils are usually very dark in color due to the high organic matter content and the presence of volcanic ash. The dark color indicates high fertility and the presence of nutrients.

- High Porosity: Volcanic soils have a high porosity, meaning they have many small spaces or pores within the soil structure. This allows for good drainage and aeration, which is beneficial for plant growth.

- Rich in Nutrients: Volcanic soils are rich in nutrients such as potassium, phosphorous, and trace elements like iron and magnesium. These nutrients are released from the volcanic ash and rocks during weathering and decomposition.

- Good Water Retention: Despite their high porosity, volcanic soils also have good water retention capacity. The fine particles of volcanic ash can hold onto water and release it slowly, ensuring a steady supply of moisture to plants.

- Lightweight: Due to the presence of volcanic ash, volcanic soils are relatively lightweight compared to other types of soils. This makes them easier to work with and allows for better root penetration.

Heading: Formation of Volcanic Soil

Volcanic soils are formed through the following processes:

1. Volcanic Activity: During volcanic eruptions, ash and lava are ejected from the volcano. The ash settles on the surrounding land and mixes with other materials, such as rocks and organic matter.

2. Weathering: Over time, the volcanic ash and rocks undergo weathering, which is the process of breaking down into smaller particles. This weathering is facilitated by factors like temperature changes, moisture, and the action of wind and water.

3. Decomposition: As the volcanic ash and rocks weather, they decompose into smaller particles and release nutrients into the soil. This decomposition is aided by microorganisms and the acidity of the volcanic materials.

4. Organic Matter Accumulation: Organic matter, such as dead plants and animals, also contribute to the formation of volcanic soil. The decomposition of organic matter adds nutrients and improves the soil structure.

Heading: Importance of Volcanic Soil

Volcanic soils have several benefits and are highly suitable for agriculture. Some of the key reasons for their importance are:

1. Fertility: The high nutrient content of volcanic soils makes them highly fertile. They provide essential nutrients to plants, promoting healthy growth and high yields.

2. Water Management: The porosity and water retention capacity of volcanic soils allow for proper drainage and moisture control. This helps prevent waterlogging and ensures that plants receive optimal amounts of water.

3. Soil Structure: Volcanic soils have a good structure, with a crumbly texture that promotes root penetration and nutrient uptake. This facilitates plant growth and development.

4. Crop Diversity: The fertility and nutrient availability of volcanic soils support a wide range of crop species. They are particularly suitable for the cultivation of crops such as coffee, cacao, and fruits like bananas and pineapples.

In conclusion, volcanic soils are characterized by their dark color, high porosity, and nutrient-rich composition. They are formed through the weathering and decomposition of volcanic ash and rocks, and