Learn Hardcore Italian: La risposta sarà firmata ufficialmente domani mattina. - The answer will be officially signed tomorrow morning.

Italian nouns generally need an article. La risposta means the reply, and the article la agrees in gender (feminine) and number (singular) with risposta.

Why is the verb phrase sarà firmata in the passive voice and future tense?

This uses the future simple of essere (sarà) plus the past participle firmata to form a passive construction. It emphasizes that the reply will receive the action of signing tomorrow, without mentioning who will sign it.

How does the past participle firmata agree with risposta?

In a passive sentence, the past participle must match the subject’s gender and number. Risposta is feminine singular, so firmata ends in -a.

Could I rewrite this in the active voice? How?

Yes. You’d need to supply or imply the doer of the action (the agent). For example:
Il direttore firmerà ufficialmente la risposta domani mattina.
Here il direttore (the director) actively performs the signing.

Why is ufficialmente placed after firmata and before domani mattina?

Adverbs like ufficialmente usually follow the verb they modify. The temporal phrase domani mattina then comes at the end to specify when the signing happens.

What’s the difference between domani mattina, domattina, and stamattina?

Domani mattina = tomorrow morning (standard)
Domattina = informal contraction of domani mattina
Stamattina = this morning (earlier today)

Why isn’t there a preposition before domani mattina?

Time expressions in Italian generally stand alone without prepositions. Domani mattina directly functions as an adverbial phrase indicating time.

What nuance does the verb firmare carry in this context?

Firmare means to sign. Here it implies an official or legal validation of the document (the reply), not just writing or approving it informally.