El detergente es mío.

Because detergente is a masculine noun in Spanish: el detergente.

This is a good reminder that nouns ending in -e are not always predictable by their ending. Some are masculine, some are feminine, so you often just have to learn the gender with the word.

Since it is masculine singular, other words connected to it also stay masculine singular:

• el detergente
• es mío

Because Spanish normally uses ser to express ownership/possession.

So:

• El detergente es mío = it belongs to me

Using estar here would sound wrong. In Spanish, ser is used for identity, origin, characteristics, and also possession in sentences like this:

• Es mío
• Es tuyo
• Es nuestro

Here mío is being used as a possessive pronoun, not a possessive adjective.

Compare:

• mi detergente = my detergent
  Here, mi goes before the noun.

• El detergente es mío = The detergent is mine
  Here, mío stands on its own after ser.

So Spanish distinguishes between:

• mi / tu / su / nuestro... before a noun
• mío / tuyo / suyo / nuestro... when the idea is mine/yours/his/hers

They both relate to possession, but they are used differently.

• mi = used before a noun

  • mi detergente

• mío = used without a noun, or after ser

  • El detergente es mío

A simple way to remember it:

• mi = my
• mío = mine

The accent mark shows the correct pronunciation: MEE-oh.

Without the accent, Spanish spelling rules would suggest a different stress pattern. The accent helps show that í and o are pronounced in separate syllables:

• mí-o

So the written accent is important for both stress and pronunciation.

Yes. Possessive forms like mío agree with the thing owned, not with the owner.

Since detergente is masculine singular, the sentence uses mío.

Other forms are:

• mío = masculine singular
• mía = feminine singular
• míos = masculine plural
• mías = feminine plural

Examples:

• La botella es mía.
• Los detergentes son míos.
• Las cajas son mías.

No, that is not how Spanish normally expresses ownership here.

For possession, Spanish would use:

• El detergente es mío
• El detergente es de Juan
• El detergente es de ella

With people’s names or pronouns like él/ella, de works fine:

• Es de ella
• Es de nosotros

But de mí is generally not used to mean mine in this kind of sentence. Spanish strongly prefers mío.

Normally, no. That sounds unnatural in standard Spanish.

Spanish usually wants the article here:

• El detergente es mío.

The article helps identify the noun as a specific thing being talked about. In English, the can sometimes feel optional in certain contexts, but in Spanish it is much more often required.

If you want to be more specific, you could also say:

• Ese detergente es mío. = that detergent is mine

A simple approximation is:

• detergente → deh-tehr-HEN-teh
• mío → MEE-oh

A few helpful notes:

• The g in detergente is like an English h sound because it comes before e
• The stress in detergente is on gen
• The stress in mío is on mí

Yes. Detergente is widely understood across Latin America.

Depending on the country and situation, people may also use more specific words, especially for cleaning products:

• detergente for detergent in general
• jabón for soap
• detergente para ropa for laundry detergent
• lavavajillas or other regional terms for dishwashing detergent

But detergente itself is a normal, standard word.

Yes. That is a very natural variation.

• El detergente es mío = the detergent is mine
• Ese detergente es mío = that detergent is mine

Using ese helps point to a specific detergent, especially if there are several items around. It is often what a speaker would say in a real situation where they are identifying one object.