Este pertence é meu.

No. In Este pertence é meu, pertence is a noun, not the verb pertencer.

• o pertence = a belonging, an item, a possession
• pertence = belongs when it is the verb

That is why the sentence also has é. The structure is:

• Este pertence = this item / this belonging
• é meu = is mine

If pertence were a verb, the sentence would have to be different, for example:

• Isto me pertence = this belongs to me
• Isso pertence a mim = this belongs to me

So here, pertence is a thing, not an action.

It is grammatically possible, but it sounds a bit formal and somewhat unusual in everyday conversation.

A Brazilian is more likely to say:

• Isso é meu.
• Este objeto é meu.
• Esse item é meu.

The noun pertence exists, but the plural pertences is much more common, especially when talking about personal belongings:

• Onde estão meus pertences? = Where are my belongings?

So the sentence is understandable, but not the most everyday phrasing.

Because este is used before a noun, while isto replaces the noun.

Here, este is directly modifying pertence:

• este pertence = this item

You cannot say isto pertence with the meaning this item if pertence is a noun right after it.

Compare:

• Este pertence é meu. = This belonging/item is mine.
• Isto é meu. = This is mine.

So:

• este
  • noun
• isto = pronoun by itself

According to traditional grammar:

• este = this, near the speaker
• esse = that, near the listener or already mentioned
• aquele = that over there, far from both

So este pertence suggests something close to the speaker.

However, in everyday Brazilian Portuguese, people often use esse where older grammar would expect este. Because of that, Esse pertence é meu may sound more natural in casual speech than Este pertence é meu.

So the short answer is:

• este is grammatically correct
• esse is very common in spoken Brazilian Portuguese

Because meu agrees with the noun pertence, not with the speaker.

Pertence is a masculine singular noun, so the possessive must also be masculine singular:

• Este pertence é meu.

If the noun were feminine, you would use minha:

• Esta mochila é minha.

Agreement works like this:

• masculine singular → meu
• feminine singular → minha
• masculine plural → meus
• feminine plural → minhas

After the verb ser, Portuguese often uses a possessive without an article:

• É meu.
• É sua.
• São nossos.

So é meu is the normal, neutral form.

You can say é o meu, but that usually adds contrast or emphasis:

• Não é o seu; é o meu. = It isn’t yours; it’s mine.

So in this sentence, é meu is the most natural choice.

Yes, but much less often than pertences in the plural.

The plural is very common for personal belongings:

• Seus pertences estão aqui.
• Pegue seus pertences.

The singular pertence can be used for one specific item, but it sounds more formal or institutional, like something you might hear in a school, office, or lost-and-found context.

In casual speech, people often prefer simpler words such as:

• objeto
• item
• coisa

Some more natural options in Brazilian Portuguese are:

• Isso é meu. — very common in speech
• Isto é meu. — correct, but less common in casual Brazilian speech
• Este objeto é meu. — clearer and more natural than pertence
• Esse item é meu. — also natural
• Isso me pertence. — grammatical, but more formal

If you want the most everyday spoken option, Isso é meu is probably the best choice in many situations.