Active voice, passive voice, adjectives transforming into verbs

Question

I am attempting to complete some simple homework examples my Russian teacher has given me. (I am learning Russian in my free time, whilst I work full-time)

The example given in my textbook is:

Given: Наша квартира была приватизирована пять лет назад.

Desired: Нашу квартиру приватизировали пять лет назад.

I require the following clarifications:

1. Is my assumption that the sentence is going from the active voice in the given sentence, to the passive voice in the desired sentence, correct?
2. What part of speech is the word «приватизирована»? (My usual search source, Wiktionary is failing me.)
3. What is happening to the above mentioned word when it moves from the given sentence to the desired sentence?
4. Why does the above mentioned word decline into the plural past tense form, whereas in the first sentence «быть» is in its feminine form?
5. How does it happen? What topic or topics must I read, to elaborate this topic further?
6. Are there any rules regarding this?

Answer 1

Наша квартира была приватизирована пять лет назад.

The sentence is in the passive voice in the past formed with быть which agrees with the subject наша квартира in gender(feminine ) = была + приватизирована (past passive participle, short form) also agreeing in gender with the subject.The topic is страдательный залог.

Нашу квартиру приватизировали пять лет назад.

The sentence is in the active voice, impersonal, past tense,formed with the verb which agrees with the "dummy" they (приватизировали), which is left out. The object is нашу квартиру (accusative sing).The topic is безличные предложения. Both sentences mean the same and have a "hidden" agent.

Answer 2

Is my assumption that the sentence is going from the active voice in the given sentence, to the passive voice in the desired sentence, correct?

Well, actually it's vice versa: passive to active.

What part of speech is the word «приватизирована»?

This is "краткое страдательное причастие" (passive participle, short form, past tense, singular, feminine).

What is happening to the above mentioned word when it moves from the given sentence to the desired sentence?

Why does the above mentioned word decline into the plural past tense form, whereas in the first sentence «быть» is in its feminine form?

This is impersonate construction which is used along with "normal" active voice plural. I.e. "[they] did" (with "they" omitted) in Russian doesn't mean anyone in particular.