Meu tio prefere ir de ônibus na terça-feira, porque a avenida fica cheia.

In Brazilian Portuguese, both meu tio and o meu tio are possible, but meu tio is very common and natural.

• meu tio = my uncle
• o meu tio = also my uncle, but with the article included

In Brazil, possessives often appear with or without the definite article, depending on region, style, and context. In a simple sentence like this, meu tio sounds completely normal.

After preferir, Portuguese often uses another verb in the infinitive to say what someone prefers to do.

So:

• preferir = to prefer
• ir = to go

Together:

• prefere ir = prefers to go

This is similar to English:

• He prefers to go by bus

Other examples:

• Ela prefere ficar em casa. = She prefers to stay home.
• Eu prefiro sair cedo. = I prefer to leave early.

Portuguese commonly uses de to express the means of transportation.

• de ônibus = by bus
• de carro = by car
• de trem = by train
• de avião = by plane

So ir de ônibus literally looks like to go of bus, but the natural English translation is to go by bus.

With transportation expressions, Portuguese normally uses de + vehicle without an article in this kind of general meaning.

So you say:

• ir de ônibus
• ir de carro
• ir de bicicleta

This means the method of travel in a general sense, not a specific bus or car.

If you were talking about a particular bus, the structure would be different, for example:

• ir no ônibus das 8 = to go on the 8 o’clock bus

The circumflex accent in ônibus shows the stressed syllable and affects pronunciation.

• ônibus is stressed on the first syllable: Ô-ni-bus

The accent helps distinguish the correct stress pattern. Portuguese spelling often marks stress when a word does not follow the most common default rules.

Na is a contraction of em + a.

• em = in, on, at
• a = the
• na = in/on the

So:

• na terça-feira = on Tuesday

In Portuguese, days of the week are often used with an article in expressions like this.

Compare:

• na terça-feira = on Tuesday
• na segunda-feira = on Monday
• no domingo = on Sunday

The weekdays from Monday to Friday are traditionally written with a hyphen:

• segunda-feira
• terça-feira
• quarta-feira
• quinta-feira
• sexta-feira

This is just the standard spelling. You should learn them as fixed forms.

Notice that sábado and domingo do not follow this pattern.

Here porque means because, so the one-word form is correct.

In Portuguese, these forms can be confusing:

• porque = because
• por que = why / for what reason
• porquê = the reason
• por quê = why, usually at the end of a question

In this sentence, the second clause gives a reason:

• porque a avenida fica cheia = because the avenue gets crowded

So porque is the correct choice.

Both can be possible, but they are not exactly the same.

• fica cheia suggests becomes or gets crowded/full
• está cheia simply says it is crowded/full

So here, fica cheia implies a change or a typical situation:

• the avenue gets crowded
• the avenue ends up crowded
• the avenue becomes full

This works very naturally when describing what usually happens on Tuesdays.

Because cheia agrees with avenida, which is a feminine noun.

• a avenida = feminine
• cheia = feminine form of full / crowded

Agreement is very important in Portuguese. Adjectives often match the noun in gender and number.

Examples:

• o ônibus cheio = the full bus
• a avenida cheia = the crowded avenue
• as ruas cheias = the crowded streets

Literally, cheia means full, but in this context it is often best understood as crowded or very busy.

So:

• a avenida fica cheia can mean
  
  • the avenue gets full
  • the avenue gets crowded
  • the avenue gets very busy

When talking about streets, avenues, buses, or places with many people or cars, English often prefers crowded or busy instead of the more literal full.

Yes, Portuguese allows some flexibility in word order.

The sentence as written is very natural:

• Meu tio prefere ir de ônibus na terça-feira...

But you could also say:

• Meu tio, na terça-feira, prefere ir de ônibus...
• Na terça-feira, meu tio prefere ir de ônibus...

The original order is simple and neutral. It keeps the main idea together:

• subject: Meu tio
• verb phrase: prefere ir de ônibus
• time expression: na terça-feira

Yes, na terça-feira is singular because it refers to Tuesday in a general or specific sense depending on context.

If you wanted to mean on Tuesdays as a repeated habit, Portuguese often uses the plural:

• às terças-feiras = on Tuesdays

So compare:

• na terça-feira = on Tuesday
• às terças-feiras = on Tuesdays

In your sentence, na terça-feira can be understood as on Tuesday or sometimes on Tuesdays, depending on context, but the most direct reading is singular.

Fica is the he/she/it form of ficar.

Ficar has several common meanings, including:

• to stay
• to become
• to end up
• to be located

In this sentence, it means to become / to get:

• a avenida fica cheia = the avenue gets crowded

This is a very common use of ficar in Brazilian Portuguese:

• Ele ficou triste. = He became sad.
• A sala fica vazia. = The room becomes empty.
• O trânsito fica ruim. = Traffic gets bad.