The correct option for the order in which soil particles settle from light to heavy when shaken with water is A: humus, clay, silt, sand, stones. Let's break down why this is the correct answer and why the other options are incorrect. Explanation of the Correct Answer (Option A)

1. Understanding Soil Composition: Soil is made up of various components, including organic matter (humus), minerals, and particles of different sizes. The main types of soil particles are:
2. Humus: This is decomposed organic matter and is very light.
3. Clay: These are very fine particles that can hold water and nutrients but are also light.
4. Silt: Slightly larger than clay, silt particles are still relatively small and light.
5. Sand: These are larger particles that are heavier than clay and silt.
6. Stones: These are the heaviest components and settle last.
7. Settling Order: When soil is shaken with water, the lighter particles will settle first. The order of settling is determined by the size and weight of the particles:
8. Humus is the lightest and will float or settle last.
9. Clay is very fine and light, so it settles next.
10. Silt is slightly heavier than clay but still light enough to settle before sand.
11. Sand is heavier than both clay and silt, so it settles after them.
12. Stones are the heaviest and will settle at the bottom.

Why Other Options Are Incorrect

• Option B: humus, silt, clay, sand, stones
• This option incorrectly places silt before clay. Silt particles are larger than clay particles, so they should settle after clay, not before.
• Option C: humus, clay, silt, stones, sand
• This option incorrectly places stones before sand. Stones are much heavier than sand and should settle last, not before sand.
• Option D: humus, sand, silt, clay, stones
• This option incorrectly places sand before both silt and clay. Sand is heavier than both of these particles and should settle after them.

Summary of Key Points

• Soil Particle Sizes: Understand the relative sizes and weights of soil components: humus (lightest), clay, silt, sand, and stones (heaviest).
• Settling Order: The correct order of settling from lightest to heaviest is humus, clay, silt, sand, and stones.
• Common Mistakes: Be careful not to confuse the sizes of clay and silt, and remember that heavier particles settle last.

Revision Summary

• Soil particles settle in the order of their weight: humus (lightest), clay, silt, sand, stones (heaviest).
• Humus is organic matter, while clay, silt, and sand are mineral particles of varying sizes.
• Always remember that heavier particles settle after lighter ones when mixed with water.
• Review the definitions and characteristics of each soil component to avoid confusion in settling order.