Sieving is a technique used to separate mixtures containing solid particles of

Analysis

The question asks for the principle behind sieving as a separation technique. We need to identify the specific property of the solid particles that allows this method to work effectively.

Concept Explanation

Sieving is a mechanical method used to separate a mixture of solids. It relies on the difference in particle size.

A sieve (or mesh) acts as a barrier with holes of a specific diameter. When a mixture is passed through the sieve:

• Particles smaller than the holes pass through (the filtrate).
• Particles larger than the holes are retained on the sieve (the residue).

If all particles were the same size, they would either all pass through or all be retained, making separation impossible. Therefore, the mixture must contain particles of varying sizes for the process to be effective.

Step-by-Step Solution

1. Identify the goal: Separate solid particles from a mixture.
2. Examine the mechanism: The sieve acts as a filter that discriminates based on physical dimensions.
3. Evaluate the options: • A & B: Simply having small or large particles doesn't guarantee separation; you need a comparison between them. • D: If particles are the same size, they cannot be separated by a sieve. • C: Because the sieve allows some particles to pass while blocking others, the mixture must contain particles of different sizes.

Conclusion

Sieving is only effective when the components of the mixture have different particle sizes, allowing the sieve to act as a size-selective barrier.

Exam Tip: Think of a kitchen sieve used for garri or flour. You are trying to separate the fine powder (small particles) from the coarse chaff or lumps (large particles). This is only possible because the mixture contains particles of different sizes!