A professora apagou a resposta errada no quadro.

In Brazilian Portuguese, it is very common to use the definite article before a noun, especially with specific people or things.

So:

• a professora = the teacher
• professora by itself can sound more general, like teacher as a role or label

In this sentence, A professora refers to a specific teacher, so a is natural.

Because professora is the feminine form of teacher, and it shows that the teacher is female.

• o professor = the male teacher
• a professora = the female teacher

Portuguese nouns often change form to match biological sex when talking about people.

Apagou is the preterite form of apagar.

Here it means the action was completed in the past:

• apagar = to erase
• apagou = erased

So this is not was erasing or used to erase. It means she erased it as a finished action.

These two forms express different kinds of past actions.

• apagou = she erased it, a completed event
• apagava = she was erasing / used to erase, ongoing, repeated, or background action

In this sentence, the idea is a single completed action, so apagou is the right choice.

Portuguese usually follows a basic subject + verb + object order here:

• A professora = subject
• apagou = verb
• a resposta errada = direct object
• no quadro = location

So the sentence structure clearly shows that the teacher performed the action.

Also, apagou is a third-person singular verb form, which matches a professora.

In Portuguese, adjectives usually come after the noun.

So the most normal order is:

• resposta errada = wrong answer

Putting the adjective before the noun is less common and can sound literary, emphatic, or stylistically marked in many cases.

So:

• a resposta errada = the normal, neutral way
• a errada resposta = unusual in everyday speech

Because adjectives in Portuguese usually agree with the noun they describe in gender and number.

Here:

• resposta is feminine singular
• so the adjective must also be feminine singular: errada

Compare:

• a resposta errada = the wrong answer
• o comentário errado = the wrong comment
• as respostas erradas = the wrong answers

Yes. In this sentence, errada modifies resposta.

That is clear because:

• it comes right after resposta
• it agrees with it in feminine singular form

So the phrase a resposta errada works as one unit: the wrong answer.

No quadro means on the board.

It is made of:

• em = in / on
• o = the
• em + o = no

So:

• no quadro = on the board

In a classroom context, quadro usually means the board, such as a whiteboard or blackboard.

Because Portuguese normally contracts certain prepositions with articles.

Here:

• em + o = no

Other common contractions are:

• em + a = na
• de + o = do
• de + a = da
• a + o = ao
• a + a = à

So em o quadro is not the normal form. No quadro is the correct one.

Yes, quadro can have other meanings depending on context, such as:

• a board
• a picture frame
• a painting
• a chart
• even a general situation or condition in some expressions

But in this sentence, because of apagou and the classroom context created by professora, the natural meaning is board.

Because Portuguese does not use a direct-object marker like Spanish often does with people.

Here, a resposta errada is simply the direct object of apagou with no extra marker needed.

So:

• A professora apagou a resposta errada = normal Portuguese structure

Yes. Portuguese allows some variation.

For example:

• A professora apagou a resposta errada no quadro.
• A professora apagou do quadro a resposta errada.
• A professora apagou a resposta errada do quadro.

These are all understandable, though the feel may differ slightly.

The original sentence is natural, but some speakers may prefer a version with do quadro when they want to emphasize that the answer was erased from the board.

A little, yes.

The most natural reading is:

• the teacher erased the wrong answer, and that answer was on the board

But because no quadro comes after a resposta errada, a learner might wonder whether it attaches to the verb or the noun phrase.

In real usage, context usually removes the doubt. In a classroom situation, the intended meaning is very clear.

Yes. Apagar is a very common verb with several meanings depending on context, including:

• to erase
• to turn off
  
  • apagou a luz = turned off the light
• to put out
  
  • apagou o fogo = put out the fire

In this sentence, because of a resposta and no quadro, the meaning is clearly erased.