Brick earth composition — Select the correct set of desirable constituents and percentages for good brick earth.

Introduction / Context:
Proper brick earth composition ensures strength, soundness on firing, resistance to cracking, and good color. Recognizing typical target ranges for key constituents aids in site selection and mix correction for brick manufacture.

Given Data / Assumptions:

• Ranges are indicative, based on conventional textbooks and practice.
• Minor constituents (alkalis, magnesia) are controlled to avoid efflorescence and deformation.

Concept / Approach:
Alumina provides plasticity; silica prevents excessive shrinkage and warping; limited lime acts as a flux promoting vitrification; iron oxide helps color and strength. Balanced proportions yield well-fired, durable bricks.

Step-by-Step Solution:
Target alumina: about 20–30% for workable plasticity.Target silica: about 50–60% to control shrinkage and impart rigidity.Limit lime: not more than ~5% to avoid friability and popping on firing.Provide iron oxide: about 5–6% for color and improved burning behavior.Therefore the aggregate “All of the above” best represents good brick earth.

Verification / Alternative check:
Firing trials show that mixes within these bands yield stable, sound bricks with good appearance.

Why Other Options Are Wrong:
Each single constituent alone is necessary but not sufficient. Optimal brick earth requires all in balanced ranges.

Common Pitfalls:
Confusing “oxide of iron” with “oxide of lime”; the former is desired in small amounts for color control.

Final Answer:
All of the above