É importante que todos fiquem em silêncio durante a prova.

Because É importante que... normally triggers the subjunctive in Portuguese.

• ficam = indicative, used for statements of fact
• fiquem = present subjunctive, used after expressions of necessity, importance, desire, doubt, etc.

So É importante que todos fiquem... means something like It is important that everyone be / stay..., which is exactly the kind of context where Portuguese uses the subjunctive.

The infinitive is ficar, meaning to stay, to remain, or sometimes to be in a certain state.

Here is the present subjunctive of ficar:

• eu fique
• você/ele/ela fique
• nós fiquemos
• vocês/eles/elas fiquem

Since todos is plural, the sentence uses fiquem.

Here que introduces a subordinate clause.

The structure is:

• É importante = it is important
• que todos fiquem em silêncio durante a prova = that everyone stay silent during the exam

So que works like that in English, even though in English it is often omitted. In Portuguese, it is required in this structure.

Because todos is grammatically plural.

• todos = all / everyone
• verb: fiquem = plural form

Even if English often uses everyone with a singular verb, Portuguese todos behaves as a plural word. So todos fiquem is the correct agreement.

Yes. Todo mundo is very common in Brazilian Portuguese and means everyone.

You could say:

• É importante que todo mundo fique em silêncio durante a prova.

Notice the difference:

• todos fiquem → plural verb
• todo mundo fique → singular verb

That is because todo mundo is grammatically singular, even though it refers to many people.

Em silêncio is a very common expression meaning in silence or silently.

So:

• ficar em silêncio = to remain silent

You could sometimes hear sentences with adjectives, but ficar em silêncio is the most natural and idiomatic choice here. It focuses on the state or behavior expected during the exam.

Durante means during.

So:

• durante a prova = during the exam

It is a preposition used to show that something should happen throughout a period of time. In this sentence, it tells you when everyone should stay silent.

Portuguese often uses the definite article where English may or may not use the.

Here, a prova refers to a specific event or situation that speaker and listener both understand: the exam.

So durante a prova is the natural way to say during the exam. Leaving out the article would sound unnatural in this sentence.

In Portuguese, prova can mean different things depending on context, including:

• test / exam
• proof / evidence

In this sentence, because of durante a prova and ficar em silêncio, it clearly means exam/test.

Yes, and that is also correct, but the structure is slightly different.

• É importante que todos fiquem em silêncio... = It is important that everyone stay silent...
• É importante ficar em silêncio... = It is important to stay silent...

The version with que todos fiquem explicitly mentions everyone and uses the subjunctive. The version with ficar is more general and uses the infinitive instead of a full clause.

This is a spelling rule in Portuguese.

The verb is ficar, but before e or i, Portuguese often changes c to qu to keep the hard k sound:

• ficar
• eu fique
• eles fiquem

If it were written with just c before e, the pronunciation would change. So qu keeps the correct sound.