A professora respondeu a muitas perguntas na aula.

Because a is the definite article, so A professora means the teacher.

In Portuguese, it is very common to use the definite article with a person or role that is already known from context. English often leaves this out in places where Portuguese keeps it.

So:

• A professora = the teacher
• Uma professora = a teacher

If the speaker is talking about a specific teacher already known in the situation, A professora is the natural choice.

Respondeu is the preterite form of responder.

It is:

• 3rd person singular
• used for a completed past action

So it means answered or responded in the sense of something that happened and is finished.

Examples:

• Ela respondeu. = She answered.
• A professora respondeu. = The teacher answered.

Here, a means to, and it comes from the way the verb responder is often used in Portuguese.

So:

• responder a uma pergunta = to answer a question
• responder ao aluno = to respond to the student

In careful or standard Portuguese, responder often takes a before what is being answered or the person being answered.

So respondeu a muitas perguntas is literally something like answered to many questions, although in natural English we just say answered many questions.

Because there is no article there.

The accent in à or às appears when two words combine:

• the preposition a
• plus the feminine article a or as

So:

• a + a = à
• a + as = às

But in a muitas perguntas, muitas is a quantifier/determiner, and there is no separate article as before it.

That is why you write:

• a muitas perguntas = correct

But you could have:

• às perguntas = to the questions

So the missing accent is not random; it shows that no article has merged there.

Because muitas must agree with perguntas.

Pergunta is:

• feminine
• plural here: perguntas

So the word for many must also be:

• feminine plural → muitas

Compare:

• muita pergunta = many/a lot of question(s) depending on context
• muitas perguntas = many questions
• muitos alunos = many students (masculine plural)

This is basic gender-and-number agreement.

Na is a contraction of:

• em
  • a = na

So na aula literally means in the class.

Depending on context, in natural English it can mean:

• in class
• during class
• in the lesson

It does not always focus on physical location only. Very often it means the event or class session itself.

So in this sentence, na aula is best understood as something like during class or in class.

Because the sentence refers to one class session.

Portuguese often uses the singular when talking about a single event or setting:

• na aula = in class / during the class
• na reunião = in the meeting
• no trabalho = at work

If you wanted the plural, it would mean multiple classes:

• nas aulas = in the classes / during classes

So na aula suggests one particular class period.

Yes. Portuguese word order is fairly flexible, although Subject + Verb + Object is the most neutral pattern here.

The original sentence:

• A professora respondeu a muitas perguntas na aula.

A very common alternative would be:

• Na aula, a professora respondeu a muitas perguntas.

Both are natural. The difference is mostly about emphasis:

• starting with A professora emphasizes who did it
• starting with Na aula emphasizes when/where it happened

Not always in real-life Brazilian Portuguese.

In more standard or careful grammar, you will often see:

• responder a uma pergunta
• responder ao aluno

But in everyday Brazilian Portuguese, many speakers also say:

• responder uma pergunta

So both patterns may appear, especially with things like pergunta.

Still, the version in your sentence, respondeu a muitas perguntas, is very natural and grammatically safe.

Yes.

The verb responder can correspond to both English verbs:

• to answer
• to respond

Which one sounds best depends on context.

In this sentence, because the object is perguntas, English would normally use answered:

• The teacher answered many questions in class.

If the sentence were about a person or a situation, responded might sound more natural.

Because muitas perguntas means many questions, not the many questions.

Here, muitas already introduces the noun phrase, so no article is needed.

Compare:

• muitas perguntas = many questions
• as perguntas = the questions
• as muitas perguntas = the many questions or the numerous questions (possible, but more specific and less neutral)

So the sentence is simply saying she answered many questions, not a specially identified set of questions.