[Corribus]

In chemistry at your level, sometimes you just have to settle for learning traits without delving too deeply the origins of rules, because the answers require a deep understanding of physical chemistry.

Oxygen likes to form two bonds, and silicon, like carbon, likes to form four. However unlike carbon, silicon does not like to form double bonds because it is a bigger atom and the p orbitals responsible for forming pi bonds are more diffuse, and so overlap between p orbitals on adjacent nuclei is poor. For this reason, CO₂ is a small molecular gas with formula O=C=O, whereas silica, which has the same type of (SiO₂) forms an extended structure characterized by single bonds between silicon and oxygen atoms. It is the only structure available that minimizes the number of pi bonds formed with silicon atoms.

Looking at your other options: (A) can't form easily an extended structure because halogens like chlorine typically (though not always) only bond 1 time each, so SiCl4 is a small molecule. This logic also extends to (C) and (D). (E) is likewise excluded because hydrogen usually only bonds once as well, and (F) involves fluorine, another halogen that is only available for a single bond to another atom. So with the exception of (B), all do not offer the ability to form extended structures because to do so would involve more bonds than the atoms involved would typically be happy to form.

[peterpan1372]

As I understood it: you mean because Si has a higher oxidation number, it forms more likely a double bond becasue of its higher number of free electrons, making it more solid?

[Babcock_Hall]

What would you consider a giant structure?  What wouldn't a giant structure be made of?  Ever see a a liquid or gas be a structure?

to first question: I already stated.
to second and third: I dont know which one of them could be gases or liquids...

You could look up which of these substances is a gas or liquid at room temperature.

[peterpan1372]

on test day, you have max. 15 sec to solve this question without internet, calculator etc...

[Corribus]

As I understood it: you mean because Si has a higher oxidation number, it forms more likely a double bond becasue of its higher number of free electrons, making it more solid?

No, the formal oxidation number of silicon has very little to do with it. And I already told you that silicon does not form double bonds easily. Honestly, though you can arrive at the correct answer of B by process of elimination. All the other options involve halogens or hydrogen atoms, which only bond once, and there's no way to make long extended networks of atoms as a result. 

[peterpan1372]

isn't there another way to get to the answer quickly?

[peterpan1372]

or other question: is there a quick way to know if a substance is made of gas, liquid, or is solid?

[peterpan1372]

you also stated: (E) is likewise excluded because hydrogen usually only bonds once as well, and (F) involves fluorine, another halogen that is only available for a single bond to another atom.

That is what I meant. Of course, when atoms bond once it is not a strong bond. But when they bond with atoms which have excessive bonds available, this bond is going to be more solid...

[Babcock_Hall]

That is what I meant. Of course, when atoms bond once it is not a strong bond. But when they bond with atoms which have excessive bonds available, this bond is going to be more solid...

I am not sure what you mean.  Double bonds are stronger than single bonds; however, the C-F bond is a single bond, and it is quite strong.

[peterpan1372]

what I mean is: obviously, Si has a higher electronic configuration than O. So the molecule is hence going to be more stronger than the rest since it has electrons available that it hasn't used.

[Corribus]

With apologies, peterpan1372, it is evident that you really lack an understanding of the most elementary concepts in chemistry and I don't think there's much I can do to help you further. I don't regard this forum as a replacement for basic instruction in your courses - we can't teach you all of chemistry here.

I would strongly suggest you find a personal tutor or ask your professor/instructor for additional intensive help outside the classroom.

[peterpan1372]

Don't get me also wrong, but tutors are helpless. Further, I don't have the money for one. I just want to, really short and understandable, why SiO2 is the right answer if one can not dispute with oxidation numbers...

[wildfyr]

I just want to, really short and understandable, why SiO2 is the right answer if one can not dispute with oxidation numbers...

Yes but what about the next question, and the next after that? You have posted many questions in the last week or so. Virtually all demonstrate a lack of understanding of basic principles which are spelled out in any introductory textbook. Please talk to your professor if you feel this material is not being covered, this is their job. We just do this with bits and pieces of our free time.

[peterpan1372]

of course, I appreciate it, but I just want a quick understandable explanation of what you wrote - nothing else.

[Borek]

a quick understandable explanation of what you wrote

Would be based on ideas you don't know - and as such would be completely useless to you.

You need to start from the beginning. You can't learn trying to solve a test in which every question - while not very hard - uses many different concepts combined. You need to learn these concepts separately before using them, and that's something that you can do only by following a textbook (or a lecture) that introduces them in some logical order, adding new steps based on what you have learned earlier.