Learn Hardcore Italian: L’imballaggio è stato preparato in ufficio ieri sera. - The packaging was prepared in the office last night.

In Italian the past passive is built with the appropriate tense of essere + past participle. Here:
• è (3rd-person sing. presente of essere)
• stato (past participle of essere used as auxiliary)
• preparato (past participle of preparare)
So è stato preparato literally means “has been prepared” or “was prepared.” Remember that the past participle must agree in gender and number with the subject.

Why is l’imballaggio written with l’ instead of lo or il?

Imballaggio is a masculine singular noun beginning with a vowel. The masculine singular article lo contracts to l’ before any vowel (e.g. l’amico, l’ufficio). You never write lo imballaggio; you always use l’imballaggio.

Why do we say in ufficio and not al ufficio or nell’ufficio?

When indicating a general location (like “at the office,” “at school,” “in town”), Italians typically drop the article after a or in:
• in ufficio (“in/at the office”)
• a scuola (“at school”)
Using nell’ufficio is grammatically correct but implies a specific office (“in the director’s office,” etc.) and is less idiomatic when you just mean “at work.”

What does ieri sera mean, and could I say ieri la sera instead?

Ieri sera means “last night” or “yesterday evening.” It’s the standard Italian expression. Saying ieri la sera is not idiomatic. If you want to vary it, you could say la scorsa sera, but most Italians stick with ieri sera.

Does the past participle preparato ever change form in this sentence? How does agreement work?

Yes—because this is a passive, the past participle agrees in gender and number with the subject. Here l’imballaggio is masculine singular, so you use preparato (–o). If the subject were feminine (e.g. la lettera), you’d write la lettera è stata preparata (–a). For plural subjects: i pacchi sono stati preparati (masc. pl.) or le scatole sono state preparate (fem. pl.).

If I want to say “by the office,” how do I add the agent in a passive sentence?

Use da + definite article + agent. Here:
L’imballaggio è stato preparato dall’ufficio.
da + l’ (elided article before vowel) = dall’ufficio.

How would you say this in the active voice in Italian?

You need to supply or imply an agent (they/we). For example:
Hanno preparato l’imballaggio in ufficio ieri sera.
or specifying the subject:
I magazzinieri hanno preparato l’imballaggio in ufficio ieri sera.

Can I use the impersonal/passive si to express the same idea?

Yes. With si the noun follows the verb, and the verb agrees in number with the noun:
Si è preparato l’imballaggio in ufficio ieri sera.
This is an impersonal passive, common in instructions or reports.