Question

Assertion (A): Free silica occurs in soil's quartz and opal.
Reason (R): Quartz consists of a continuous framework of silica tetrahedra.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Free silica is commonly found as quartz and opal; quartz has a strong tetrahedral SiO$_4$ network.

Answer 1

The Correct Option is A

Step 1: Free silica means \( \text{SiO}_2 \) not bound in a silicate lattice, quartz and opal are its soil forms.
Step 2: Quartz's tetrahedra share all four corner oxygens, forming a continuous 3D framework.
Step 3: This structure is exactly why quartz counts as free silica, so R explains A.
Step 4: Both statements true, R is the correct explanation, matching the first option.