Virtual Quiz: the nature of conducting materials*

Yesterday we had a virtual quiz, which is a quiz you do on your own. It shows what material we are currently covering and emphasizing and, like a real quiz, contains material you may be tested on in the future. I hope you all do well on this "virtual quiz". In fact, we are giving everyone 100% ...
(PS. I added two extra problems over what we showed in class.)
(*edited, Sunday, Feb 22)

Problem 1. a) Describe the nature of copper (Cu) and aluminum (Al) paying particular attention to how many electrons remain localized (with an atom core) and how many electrons go into non-localized states and become part of the electron sea. Which electrons enable the conduction of electricity?
b) Do the electrons go into the electron sea when a voltage is applied, or are they always there waiting to conduct electricity?
c) Why is it difficult to explain in simple terms why some electrons leave their atoms and go into the non-local states of the electron sea? What is the benefit for that? What is the reason or motivation for some electrons to do that?

2. a) Describe the nature of pure silicon (Si). How many electrons does it have? What are their roles?
b) What happens when you mix in some phosphorous (P) atoms in silicon? Suppose the phosphorous atoms substitute for some of the Si atoms. How and why does that change the nature of the material and how does it effect its conductivity? (How many electrons does a P atom have?)

[Note that silicon (Si) is an element and an elemental material and not related at all to silicone (sealent), which is a complex, soft polymer material. Si, on the other hand, is the 14 element of the periodic table and forms a crystalline solid which is dark grey, shiny, has a hard surface and is somewhat brittle.]

3. (extra credit) What is something unusual about the microscopic nature of conduction in a superconductor?? What is an interested macroscopic (phenomenological*) feature in the of a superconductor?

* Phenomenological is a big word that refers to ordinary impressions of what something is like. As in, for example, "genotype and phenotype" where genotype refers to the microscopic nature of the base-pair sequence in the genome, and phenotype means what something looks like, etc, as in " a dog has four legs, etc".