Draw the three-dimensional structure of silicon dioxide.

What would be the products for the following reactions respectively? (water molecules would be the expected biproduct)

$\left(\mathrm{i}\right) {\mathrm{SiO}}_2+2\mathrm{NaOH}\to ?$

$\left(\mathrm{ii}\right) {\mathrm{SiO}}_2+4\mathrm{HF}\to ?$

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): In expensive scientific instruments, silica gel is kept in watch-glasses or in semipermeable membrane bags.

Reason (R): Silica gel adsorbs moisture from air via adsorption, thus protects the instrument from water corrosion (rusting) and / or prevents malfunctioning.

In the light of the above statements, choose the correct answer from the options given below:

Explain the structure of silica. How does it react with a. $\mathrm{NaOH}$ and b. $\mathrm{HF}$.

${\mathrm{CaF}}_2+{\mathrm{H}}_2{\mathrm{SO}}_4\to \mathrm{A}+\mathrm{D}$

${\mathrm{SiO}}_2+\mathrm{A} \left(\mathrm{excess}\right)\to \mathrm{C}$

In the above reaction, the compound $\mathrm{C}$ contains 

Identify true statement: