Explanation:

Ploughing is a common agricultural practice that involves breaking up the soil in order to prepare it for planting crops. One of the tools used during ploughing is a plank, which is used to break the soil crumbs into different sizes.

Importance of Breaking Soil Crumbs:

When soil is ploughed, it often forms clumps or crumbs. These crumbs can vary in size and texture, and breaking them up is essential for several reasons:

1. Improved Soil Structure: Breaking up soil crumbs helps improve the overall structure of the soil. It allows for better aeration and water infiltration, which are crucial for root development and nutrient uptake by plants.

2. Increased Soil Fertility: By breaking up the soil crumbs, nutrients that may be trapped within them are released and made more available to plants. This can enhance the fertility of the soil and promote healthy plant growth.

3. Reduced Soil Erosion: Soil crumbs can create a rough surface that is susceptible to erosion by wind and water. Breaking them up helps to create a smoother surface, reducing the risk of erosion and soil loss.

The Role of a Plank:

During ploughing, a plank is used to break up the soil crumbs. The plank is typically dragged behind a tractor or animal-drawn plough and exerts pressure on the soil as it moves along. This pressure causes the soil crumbs to break apart, resulting in finer soil particles.

Why Fine Soil is the Correct Answer:

The correct answer to the question is option 'B' - Fine soil. When the plank is used to break up the soil crumbs, it breaks them down into smaller particles, resulting in fine soil. Fine soil is desirable for planting as it provides a good environment for seed germination and root growth.

Other Options:

The other options listed - stones, gritty soil, and mud - are not the correct answer because they do not accurately describe the result of using a plank during ploughing.

- Stones: Planks are not used to break soil crumbs into stones. Stones are typically removed from the soil during the ploughing process.

- Gritty Soil: While ploughing can alter the texture of the soil, the primary purpose of using a plank is to break up soil crumbs into finer particles, not gritty soil.

- Mud: Planks do not create mud during ploughing. Mud is a result of soil becoming saturated with water, not from breaking up soil crumbs.

In conclusion, during ploughing, a plank is used to break up soil crumbs into fine soil. This process improves soil structure, increases fertility, and reduces the risk of erosion.