Which of the following ingredients of the brick earth enables the brick to retain its shape?

Answer: Option B

Silica is the correct answer because it enables the brick to retain its shape during the drying and burning process. Pure clay tends to shrink considerably as it dries, which can lead to cracking, warping, or distortion. Silica acts as a stabilizing material that minimizes this shrinkage, allowing the brick to maintain its original dimensions and shape.

A suitable proportion of silica also increases the hardness, strength, and durability of bricks. However, excessive silica can make bricks brittle and difficult to bind properly with mortar.

Why the Other Options are Incorrect:

Alumina: Alumina imparts plasticity to brick earth, making it easy to mould into the desired shape. Although plasticity helps in forming the brick, it is not responsible for retaining the shape during drying and burning. In fact, excessive alumina causes excessive shrinkage, which may result in cracks and deformation.

Iron Oxide: Iron oxide mainly imparts the characteristic red color to bricks and acts as a flux during burning, improving hardness and strength. It does not help the brick retain its shape.

Magnesia: Magnesia reduces shrinkage to a limited extent and may impart a yellowish tint to bricks. It also improves durability in small quantities. However, it is not the primary ingredient responsible for shape retention, and excessive magnesia can weaken the brick and cause decay over time.

Key Point to Remember:

Alumina = Plasticity (easy moulding)
Silica = Shape retention (prevents shrinkage and warping)
Iron Oxide = Color, hardness, and strength
Magnesia = Reduces shrinkage slightly and gives a yellow tint

Therefore, Silica is the ingredient of brick earth that enables the brick to retain its shape, making Option B the correct answer.