Question

Consider the following statements: Statement I: Silica in its normal form is almost non-reactive because of very high Si-O bond enthalpy.  Statement - II: Silica has no reaction with HF.  The correct answer is:

• A. Both the statements I & II are correct.
• B. Statement I is correct but statement - II is NOT correct.
• C. Statement I is NOT correct but statement - II is correct.
• D. Both the statements I & II are NOT correct.

Hint:

Silica resists nearly all acids except HF, which attacks it readily due to the strong affinity between silicon and fluorine.

Answer 1

The Correct Option is B

Step 1: Concept
Silica ($SiO_{2}$) has a network covalent structure that exhibits distinct chemical reactivity trends owing to its high bond dissociation energy, though it remains vulnerable to specific strong reagents like hydrofluoric acid.

Step 2: Meaning
Reactivity is heavily dictated by bond strength. A high bond enthalpy makes a substance relatively inert under standard circumstances, but exceptions occur when exceptionally stable compounds like $SiF_{4}$ can be generated.

Step 3: Analysis
Statement I is correct because the $Si-O$ covalent network has a very high bond enthalpy, rendering quartz/silica inert to most acids and halogens at typical temperatures. However, Statement II is false because silica readily reacts with hydrofluoric acid ($HF$) to yield silicon tetrafluoride and hexafluorosilicic acid ($H_{2}SiF_{6}$), a property commonly exploited for etching glass. $SiO_{2} + 4HF \longrightarrow SiF_{4} + 2H_{2}O$

Step 4: Conclusion
This confirms that Statement I is fully correct, whereas Statement II is incorrect.

Final Answer: (B)