O bairro fica mais silencioso à noite.

In this sentence, fica means something like becomes or gets.

So:

O bairro fica mais silencioso à noite
= The neighborhood gets quieter at night

This is a very common use of ficar in Portuguese: it can show a change of state.

Examples:

• Fico cansado depois do trabalho. = I get tired after work.
• A rua fica vazia de manhã cedo. = The street gets empty early in the morning.

So here, the idea is not just stays, but becomes / tends to be quieter at night.

In Portuguese, mais usually comes before the adjective when making a comparative.

So:

• mais silencioso = quieter / more quiet
• mais bonito = prettier / more beautiful
• mais rápido = faster

Putting mais after the adjective would sound wrong in standard Portuguese.

Because silencioso agrees with o bairro.

• bairro is a masculine singular noun
• the adjective must match it

So:

• o bairro silencioso
• o bairro fica mais silencioso

If the noun were feminine, you would use silenciosa:

• A rua fica mais silenciosa à noite.

Portuguese usually uses articles more often than English.

So O bairro is the normal way to say the neighborhood.

Without the article, bairro would usually sound incomplete in a sentence like this, unless it were part of a title, label, or a very specific stylistic context.

Compare:

• O bairro é tranquilo. = The neighborhood is calm.
• Bairro tranquilo = calm neighborhood / neighborhood area (more like a label or heading)

À noite means at night.

The à is a contraction of:

• a (a preposition)
• a (the feminine article)

This contraction is called crase, and it is written with a grave accent: à.

You do not need to translate it literally word-for-word. Just learn à noite as a common expression meaning at night.

Other common time expressions:

• de manhã = in the morning
• à tarde = in the afternoon
• à noite = at night

Yes. In Brazilian Portuguese, both à noite and de noite are common.

In many contexts, they mean basically the same thing:

• O bairro fica mais silencioso à noite.
• O bairro fica mais silencioso de noite.

Both sound natural in Brazil.
However, à noite is often taught first and is very common in neutral written Portuguese.

Each verb gives a slightly different idea:

• ser describes a more general or permanent characteristic
• estar describes a current state
• ficar often suggests becoming or ending up in a state

So:

• O bairro é silencioso.
  = The neighborhood is quiet.
  This sounds like a general characteristic.

• O bairro está silencioso.
  = The neighborhood is quiet.
  This sounds like it is quiet right now.

• O bairro fica mais silencioso à noite.
  = The neighborhood gets quieter at night.
  This suggests a change that happens at night.

So ficar is a very good choice here because the sentence is about how the neighborhood changes depending on the time.

Portuguese often forms comparisons with mais + adjective, even when English uses a special comparative form like quieter, faster, or smaller.

Examples:

• mais silencioso = quieter
• mais rápido = faster
• mais pequeno is possible in some varieties, though menor is more common for smaller

So even if English uses -er, Portuguese often just uses mais.

Yes, that is completely correct.

Both are natural:

• O bairro fica mais silencioso à noite.
• À noite, o bairro fica mais silencioso.

The second version emphasizes the time a bit more because it puts à noite first.

Portuguese allows this kind of flexibility quite naturally.

In Brazilian Portuguese, bairro is pronounced roughly like BAI-nyoo, though the exact sound is different from English.

A few points:

• bai sounds like bye
• rr in Brazil is often pronounced like an English h sound, especially in the middle of a word
• ro here is reduced, so the ending may sound closer to roo or ru

A rough approximation for English speakers is:

• BAI-hu or
• BAI-oo with a breathy r

The important thing is that rr is not pronounced like the English r in red.

Yes, but the meaning changes a little.

• silencioso = silent / quiet in terms of noise
• calmo = calm
• tranquilo = peaceful / calm / quiet
• quieto usually describes a person or thing being still, and is less natural for a neighborhood in this sentence

So for noise level, silencioso is a very good choice.

Examples:

• O bairro fica mais tranquilo à noite. = The neighborhood gets more peaceful at night.
• O bairro fica mais calmo à noite. = The neighborhood gets calmer at night.

Those are natural too, but silencioso focuses most clearly on sound.

It normally expresses a general tendency or habitual situation:

The neighborhood gets quieter at night.

So it means this is what generally happens, not just on one particular night.

Portuguese often uses the present tense for this kind of general truth or repeated pattern.

If you wanted to talk about one specific night, the context would usually make that clear, or you might use a past tense:

• O bairro ficou mais silencioso naquela noite. = The neighborhood got quieter that night.