Interrogative pronouns introduce direct or indirect questions and help identify person, thing, quantity, place, time, manner, and cause. They relate to Pronomes because they substitute or point to an unknown term, but here they are used to request information. In interrogative structures, they also interact with the sentence order and with intonation to mark the question naturally.

What asks about a thing, idea or fact, while who asks about a person. In informal register, que can appear referring to people, but that use is not the most recommended in the careful variety. Quem can also occur in constructions with a preposition when the question requires a complement introduced by a specific grammatical relation.

IdeiaIdea	ExemploExample
que pergunta por coisawhat asks about a thing	O que aconteceu?What happened?
quem pergunta por pessoawho asks about a person	Quem chegou cedo?Who arrived early?
que em uso informal para pessoaque in informal use for a person	Que falou comigo?Que spoke to me?

Which and which serve to choose among options or identify a specific element within a set. These forms agree in number with the noun they accompany, and qual can also appear isolated when the referent is already clear in context. When the choice falls on an expressed name, the agreement helps to make the question more precise.

IdeiaIdea	ExemploExample
qual com singularwhich with singular	Qual livro você quer?Which book do you want?
quais com pluralwhich with plural	Quais caminhos levam ao centro?Which paths lead to the center?
qual isolado quando o contexto é conhecidowhich isolated when the context is known	Qual você prefere?Which one do you prefer?

How much, how many, how many and how many ask about quantity and agree with the noun when they function as determiners. The chosen form depends on the gender and number of the noun being asked about, and this applies to both people and things. When the quantity is treated more generally, the form can appear without an expressed noun if the context already indicates it.

IdeiaIdea	ExemploExample
quanto com masculino singularhow much with masculine singular	Quanto dinheiro falta?How much money is missing?
quantas com feminino pluralhow many with feminine plural	Quantas folhas caíram?How many sheets fell?
quantos com masculino pluralhow many with masculine plural	Quantos alunos vieram?How many students came?

Where asks for place in the sense of position, while to where asks for direction or destination. When and how are interrogative pronouns of time and manner, respectively, and help locate the event in time or describe the way in which something happens. In everyday speech, the distinction between where and to where can be less rigid, but the difference remains important in formal written standard.

IdeiaIdea	ExemploExample
onde indica posiçãowhere indicates position	Onde está a chave?Where is the key?
aonde indica direçãoto where indicates direction	Aonde você vai?Where are you going?
quando pergunta por tempowhen asks for time	Quando começa a aula?When does the class start?
como pergunta por modohow asks for manner	Como você fez isso?How did you do that?

Why, why (with a diacritic), because and porquê form a set that expresses cause, motive or explanation, but each form occupies a different role in the sentence. Why typically appears in questions and in contexts equivalent to por qual razão, por quê occurs at the end of the question or isolated with an interrogative value, because introduces explanation and porquê functions as a noun. This difference is essential for writing questions and answers with precision.

IdeiaIdea	ExemploExample
por que em pergunta diretapor que in direct question	Por que você saiu cedo?Why did you leave early?
por quê no final da perguntapor quê at the end of the question	Você saiu cedo por quê?Why did you leave early?
porque introduz explicaçãoporque introduces explanation	Saí cedo porque estava cansado.I left early because I was tired.
porquê como substantivoporquê as a noun	Não entendi o porquê da demora.I did not understand the reason for the delay.

Some interrogatives appear combined with prepositions to mark the relation required by the verb or by the noun phrase. Thus, to whom asks for the recipient, of whom asks for the origin or possession, for what asks for the purpose and with whom asks for company. These combinations are very frequent in formal questions and help maintain the correct regency (governing) and are also seen in Perguntas.

IdeiaIdea	ExemploExample
a quem pede destinatárioto whom asks recipient	A quem você entregou o pacote?To whom did you deliver the package?
de quem pede origem ou posseof whom asks origin or possession	De quem é esta pasta?Whose folder is this?
para que pede finalidadefor what asks purpose	Para que serve esta chave?What is this key for?
com quem pede companhiawith whom asks company	Com quem você veio?With whom did you come?

The question can start with the interrogative or, in more colloquial speech, can keep the order closer to the statement and depend on intonation to mark the question. In emphatic questions, the construction 'quem é que' or other sequences with 'é que' appears, very common in speech and in several regions. The placement of the interrogative should follow the desired focus, but the function of each form remains the same. Mastery of these positions also helps in using Interrogative Adverbs and in organizing Confirmation Questions.

IdeiaIdea	ExemploExample
interrogativo no início da perguntainterrogative at the start of the question	Quando você chega?When do you arrive?
entonação marca pergunta em ordem próxima da afirmativaintonation marks the question in an order close to the affirmative	Você chega quando?When do you arrive?
quem é que dá ênfase coloquialquem é que gives colloquial emphasis	Quem é que ligou?Who is it that called?