Maio é o mês de que minha mãe mais gosta, porque o clima fica mais agradável.

Because the verb gostar requires the preposition de.

• gostar de + noun/pronoun
• minha mãe gosta de maio
• So when maio becomes the thing being referred to by a relative clause, the de has to stay:

Maio é o mês de que minha mãe mais gosta.
= May is the month that my mother likes the most.

This is very common in Portuguese: if the verb needs a preposition, the relative pronoun keeps it.

You could also say:

• Maio é o mês do qual minha mãe mais gosta.

That is more formal/stiffer, but grammatically correct.

In everyday speech, many Brazilians might say o mês que minha mãe mais gosta, leaving out de, but in standard grammar de que is the expected form.

Strictly speaking, because gostar is not just to like in Portuguese; it is gostar de.

So:

• Ela gosta de maio.
• not Ela gosta maio.

That is why standard Portuguese keeps the preposition in the relative clause:

• o mês de que minha mãe mais gosta

However, in casual spoken Brazilian Portuguese, dropping the preposition is fairly common, so learners may hear:

• o mês que minha mãe mais gosta

But if you want the grammatically standard version, use de que.

Both patterns can exist, but minha mãe mais gosta is very natural in this kind of sentence.

Compare:

• o mês de que minha mãe mais gosta
• o mês de que minha mãe gosta mais

Both can mean the month my mother likes the most.

The version with mais before gosta is especially common in relative-clause structures like this. It sounds smooth and idiomatic.

So as a learner, it is best to recognize:

• de que ela mais gosta = that she likes the most

Because the two mais do different jobs.

1. minha mãe mais gosta
   Here mais means the most.
   It shows a superlative idea:

   • the month she likes the most

2. fica mais agradável
   Here mais means more.
   It forms a comparative:

   • the climate becomes more pleasant

So:

• first mais = most
• second mais = more

Because ficar here means to become, to get, or to turn.

So:

• o clima é agradável = the climate is pleasant
• o clima fica mais agradável = the climate gets/becomes more pleasant

Using fica emphasizes a change in condition. It suggests that in May, the weather/climate becomes nicer than before.

This is a very common use of ficar in Portuguese:

• A cidade fica linda à noite. = The city becomes/looks beautiful at night.
• Ele ficou triste. = He became sad.

Agradável is an adjective that has the same form for masculine and feminine singular.

So you get:

• clima agradável (masculine singular)
• temperatura agradável (feminine singular)

Only the plural changes:

• climas agradáveis
• temperaturas agradáveis

In the sentence, clima is singular, so:

• mais agradável = more pleasant

In Portuguese, months are usually used without an article when you are simply naming them.

• Maio é bonito aqui.
• Janeiro é muito quente.

So Maio é o mês... is perfectly normal.

Sometimes in Portuguese you may see an article with certain time expressions depending on the structure, but here the plain month name without an article is the natural choice.

Because Portuguese normally uses the definite article in this structure:

• Maio é o mês...
• literally: May is the month...

Using o makes it sound complete and natural. Portuguese often uses articles in places where English does too, and sometimes even where English does not.

Here, o mês is exactly what you would expect.

Porque means because when it introduces a reason or explanation.

So:

• Maio é o mês de que minha mãe mais gosta, porque o clima fica mais agradável.
• May is the month my mother likes the most, because the climate becomes more pleasant.

Learners often confuse the forms:

• porque = because
• por que = why / for which reason
• por quê = why at the end of a sentence
• porquê = the reason

In this sentence, the meaning is clearly because, so porque is correct.

Sometimes, yes, but they are not exactly the same.

• clima = climate or general weather conditions
• tempo = often weather in everyday Portuguese

So a Brazilian might naturally say:

• porque o tempo fica mais agradável

That would usually sound very natural in conversation.

The original sentence with clima is also correct, but it can sound a little broader or slightly more formal depending on context.

In Brazilian Portuguese, both are possible:

• minha mãe
• a minha mãe

Portuguese often allows a definite article before possessives, but in Brazil it is very common to omit it, especially in everyday speech.

So both of these are natural:

• minha mãe gosta de maio
• a minha mãe gosta de maio

The version without the article is very common and completely correct.

They help show pronunciation and stress.

• mês has ê, which indicates a stressed vowel sound.
• mãe has ã, which shows nasalization.

Very roughly:

• mês sounds like mess but with a more closed vowel
• mãe is nasal, somewhat like my said through the nose, though not exactly the same

These accents are important because they are part of the correct spelling and often affect pronunciation and meaning.

It is mostly neutral, but the structure o mês de que minha mãe mais gosta sounds a bit more careful or polished than very casual everyday speech.

A more conversational Brazilian version might be:

• Maio é o mês que minha mãe mais gosta, porque o clima fica mais agradável.

Or even:

• Maio é o mês que a minha mãe mais gosta, porque o tempo fica mais agradável.

So the original sentence is natural and correct, but slightly more standard in grammar because it keeps the preposition de with gostar.