Marta vive in un monolocale piccolo ma luminoso.

Vive is the third-person singular form of the verb vivere (to live).

• vivere = the infinitive, like to live
• vive = he/she lives

Since the subject is Marta, you need the form that means Marta lives:

• Io vivo = I live
• Tu vivi = you live
• Lui/lei vive = he/she lives

So Marta vive = Marta lives.

Italian uses in to say where someone lives or is located in many cases.

So:

• vive in una casa = lives in a house
• vive in un appartamento = lives in an apartment
• vive in un monolocale = lives in a studio apartment

Here, in works like English in.

Monolocale is an Italian noun for a studio apartment or one-room apartment.

It usually means the main living/sleeping area is all one room, with separate bathroom facilities.

It is a very common housing word in Italian, so it is worth learning as a set phrase:

• un monolocale = a studio apartment

Italian uses:

• un before most masculine singular nouns
• uno before masculine singular nouns beginning with certain sounds, such as s + consonant, z, ps, gn, and a few others

Since monolocale begins with m, you use un:

• un monolocale
• un libro
• un ragazzo

But:

• uno studente
• uno zaino

So un monolocale is correct.

In Italian, adjectives often come after the noun.

So:

• un monolocale piccolo
• una casa grande
• un giardino bello

This is very normal in Italian, even though English usually puts adjectives before the noun.

In this sentence, piccolo and luminoso both describe monolocale.

Adjectives in Italian must agree with the noun in gender and number.

Monolocale is masculine singular, so the adjectives must also be masculine singular:

• piccolo = masculine singular
• luminoso = masculine singular

Compare:

• un monolocale piccolo e luminoso
• una casa piccola e luminosa

If the noun were feminine, the adjectives would change.

Ma means but.

So the sentence is presenting a contrast:

• piccolo ma luminoso = small but bright

This suggests that although the apartment is small, it has the positive quality of being bright.

If it said piccolo e luminoso, it would simply list two qualities:

• small and bright

So ma adds a stronger contrast.

Because piccolo and luminoso are both directly describing the noun monolocale.

So this structure is:

• un monolocale piccolo ma luminoso

This means:

• a small but bright studio apartment

You do not need another verb like è here.

If you wanted to make it a separate statement, then you would need a verb:

• Il monolocale è piccolo ma luminoso.
  = The studio apartment is small but bright.

But in the original sentence, the adjectives are simply part of the noun phrase.

Yes, in many contexts you could say abita.

• Marta vive in un monolocale...
• Marta abita in un monolocale...

Both can mean Marta lives in a studio apartment.

A small nuance:

• vivere is the general verb to live
• abitare often focuses a bit more on residing somewhere

In everyday Italian, both are common, and in this sentence either would sound natural.

No. The verb form vive does not show gender.

It can mean:

• he lives
• she lives

We know the subject is female only because the name is Marta.

This is normal in Italian: verbs change for person and number, but usually not for gender.

Yes, it is completely natural.

The structure is:

• Marta = subject
• vive = verb
• in un monolocale piccolo ma luminoso = prepositional phrase describing where she lives

Italian often uses this straightforward order:

Subject + verb + place/explanation

So the sentence sounds normal and idiomatic.