Question

Which impurity in Silica sand must be avoided for glass making?

• A. Sodium chloride
• B. Calcium oxide
• C. Potassium oxide
• D. Iron oxide

Hint:

Iron oxide is an undesirable impurity in silica sand because it colors the glass.

Answer 1

The Correct Option is D

Concept: Silica sand is the main source of \(SiO_2\) in glass making. It must be pure, especially for clear and colorless glass.

Step 1: Iron oxide is a common impurity in silica sand.

Step 2: Even small amounts of iron oxide can impart greenish or brownish color to glass.

Step 3: This is undesirable when making clear or colorless glass.

Step 4: Therefore, iron oxide impurity must be avoided in silica sand for glass making. Hence, the correct answer is: \[ \boxed{\text{Iron oxide}} \]