A prova está difícil hoje.

Because prova is a feminine singular noun, and here it means the test/exam, not just test in a general sense.

• a prova = the test
• uma prova = a test
• prova by itself can appear in some contexts, but in this sentence Portuguese normally uses the article.

Portuguese uses definite articles more often than English does, so a prova sounds very natural.

This is one of the most common questions in Portuguese.

Here, está difícil suggests a temporary or current condition: the test is difficult today / feels difficult today.

• estar is often used for states or conditions
• ser is often used for more permanent or defining characteristics

So:

• A prova está difícil hoje. = The test is difficult today / seems hard today.
• A prova é difícil. = The test is difficult in general.

In real life, the line is not always perfectly rigid, but in this sentence está is the natural choice because hoje points to the situation right now.

You could, but it changes the feel of the sentence and is less natural in many situations.

• A prova está difícil hoje sounds like the speaker is experiencing it now and finding it hard.
• A prova é difícil hoje sounds more unusual, because hoje goes better with a temporary condition, which is why estar fits better.

So if you are talking about how hard the exam feels right now, está difícil is the best choice.

Good question. Some adjectives in Portuguese have the same form for masculine and feminine in the singular, and difícil is one of them.

So you get:

• o teste difícil
• a prova difícil

No change in the adjective.

But in the plural, it does change:

• prova difícil
• provas difíceis

So the adjective does agree in number, but not in gender here.

The accent mark shows the stressed syllable.

difícil is stressed on the fí syllable:

• di-FÍ-cil

Without the accent, a learner might be tempted to stress it incorrectly.

The accent is also part of the correct spelling, so it should always be written: difícil.

Yes. Prova can mean different things depending on context.

Common meanings include:

• test / exam
• proof / evidence
• sometimes sample / tasting / trial, depending on context

In A prova está difícil hoje, the most natural meaning is test or exam, because estar difícil hoje fits that context very well.

So prova is one of those words whose meaning depends heavily on the situation.

Because that is a very natural place for time expressions in Portuguese.

• A prova está difícil hoje.
• Hoje a prova está difícil.

Both are correct.

The difference is mostly emphasis:

• A prova está difícil hoje. = neutral, everyday word order
• Hoje a prova está difícil. = puts more focus on today

So the sentence-final hoje is normal and common.

Portuguese often leaves out subject pronouns when the subject is already clear.

In this sentence, the subject is A prova, so there is no need for a separate pronoun like ela.

• A prova está difícil hoje. = natural
• Ela está difícil hoje. = possible only if it is already very clear that ela refers to a prova

Portuguese usually prefers the noun itself unless there is a reason to replace it with a pronoun.

Yes, very common.

Portuguese often uses estar + adjective to describe how something feels at the moment.

Examples:

• O exercício está fácil. = The exercise is easy.
• A aula está interessante. = The class is interesting.
• A situação está complicada. = The situation is complicated.

So A prova está difícil hoje follows a very common and useful pattern.

In Brazilian Portuguese, está is usually pronounced roughly like es-TAH, with the stress on the last syllable.

A few helpful points:

• the á shows the stressed syllable
• the final vowel is open
• in casual speech, está may sound a bit reduced depending on the speaker, but learners should aim for the clear form first

So:

• está → stress on tá
• difícil → stress on fí

Those stress patterns are important for sounding natural.