O queijo ficou duro.

O queijo means the cheese.

Portuguese usually uses the definite article (o, a, os, as) more often than English does. So where English might say cheese got hard, Portuguese often says the cheese got hard: O queijo ficou duro.

If you say just queijo, that can sound more generic, like cheese as a substance or category, depending on context.

Here, ficou means became or got.

The verb is ficar, which has several meanings depending on context, including:

• to stay
• to remain
• to become
• to end up

In O queijo ficou duro, it means that the cheese changed state: it became hard.

Because ficou emphasizes a change.

Compare:

• O queijo é duro = The cheese is hard
  This sounds like a general characteristic.
• O queijo está duro = The cheese is hard
  This describes its current state.
• O queijo ficou duro = The cheese got/became hard
  This shows that it was not hard before, but then changed.

So ficou is the best choice when you want to express became/got.

Because duro agrees with queijo, and queijo is a masculine noun.

In Portuguese, adjectives usually agree in gender and number with the noun:

• o queijo duro = the hard cheese
• a pedra dura = the hard stone
• os queijos duros = the hard cheeses
• as pedras duras = the hard stones

So here:

• queijo = masculine singular
• duro = masculine singular

No. Duro can have several meanings depending on context.

Common meanings include:

• hard physically
  
  • pão duro = hard bread
• tough/difficult
  
  • Foi um ano duro = It was a tough year
• strict/harsh
  
  • Ele é duro com os filhos = He is strict with his children
• in some contexts, broke or without money in informal Brazilian Portuguese
  
  • Estou duro = I’m broke

But in O queijo ficou duro, it clearly means physically hard.

A rough Brazilian Portuguese pronunciation is:

oo KAY-zhoo fee-KOH DOO-roo

A few notes:

• queijo sounds roughly like KAY-zhoo
• ficou has stress on the last syllable: fi-KOU
• duro has stress on du: DU-ro

The r in Brazilian Portuguese varies by region, but in many accents the r in duro is softer than an English r.

This is the normal Portuguese order:

subject + verb + adjective/complement

So:

• O queijo = subject
• ficou = verb
• duro = complement describing the new state

This is the most natural, neutral order in Portuguese.

Yes, absolutely.

Both are natural, but they mean slightly different things:

• O queijo está duro = The cheese is hard.
  You are describing how it is now.
• O queijo ficou duro = The cheese got hard / became hard.
  You are describing a change.

If you want to stress that it hardened over time, ficou duro is better.

Yes. Both are good translations.

• became hard is a bit more neutral or formal
• got hard is more natural in everyday English

Both match ficou duro well.

Ficou is the preterite form of ficar for ele/ela/você.

So:

• eu fiquei = I became / I stayed
• você/ele/ela ficou = you/he/she became / stayed
• nós ficamos = we became / stayed
• eles/elas/vocês ficaram = they/you all became / stayed

In this sentence, o queijo is a third-person singular subject, so we use ficou.

Yes, O queijo endureceu also means The cheese hardened.

The difference is mainly style and verb choice:

• O queijo ficou duro = The cheese got hard / became hard
• O queijo endureceu = The cheese hardened

Ficou duro is very common and conversational.
Endureceu is also correct, but a little more specific and sometimes slightly less everyday in simple speech.

Yes, it is completely natural.

A Brazilian speaker might use it in situations like:

• cheese left out too long
• cheese dried out in the fridge
• cheese changed texture after cooking or cooling

It is a normal, everyday sentence.

Not always. Ficar is very common and very flexible, so its meaning depends on context.

For example:

• Fiquei em casa. = I stayed at home.
• Onde fica o banco? = Where is the bank located?
• Ela ficou feliz. = She became happy.
• O leite ficou azedo. = The milk went sour.

So in many sentences ficar means to become, but not in all of them. Context is the key.