The correct answer is C. 30%.
Clay and silt are the two main components of brick earth. Clay is a fine-grained mineral that is plastic when wet and hardens when fired. Silt is a fine-grained mineral that is not as plastic as clay, but it still hardens when fired.
The ideal clay and silt content for brick earth is 30%. This will give the brick earth the right balance of plasticity and strength. If the clay and silt content is too low, the brick earth will be too weak. If the clay and silt content is too high, the brick earth will be too difficult to work with.
The other options are incorrect because they do not represent the ideal clay and silt content for brick earth. Option A is too high, option B is too low, and option D is not specific enough.
Here is a brief explanation of each option:
- Option A: 50%. This is too high a clay and silt content for brick earth. If the clay and silt content is too high, the brick earth will be too difficult to work with. It will also be more likely to crack when fired.
- Option B: 40%. This is too low a clay and silt content for brick earth. If the clay and silt content is too low, the brick earth will be too weak. It will also be more likely to crumble when fired.
- Option C: 30%. This is the ideal clay and silt content for brick earth. It will give the brick earth the right balance of plasticity and strength.
- Option D: 25%. This is not specific enough. It does not state whether the 25% is the clay content, the silt content, or both.