Mi hermano pequeño trabaja en la ciudad.

Because mi without an accent is the possessive adjective meaning my.

• mi hermano = my brother
• mí with an accent is a pronoun used after prepositions:
  • para mí = for me
  • a mí = to me

So here, mi is correct because it is directly describing the noun hermano.

In Spanish, a possessive adjective like mi, tu, su, nuestro normally replaces the article.

So Spanish says:

• mi hermano = my brother

not:

• el mi hermano ❌

This is different from English, but it is the normal pattern in Spanish.

In Spanish, many adjectives often come after the noun they describe.

So:

• hermano pequeño = literally brother small

This is the normal word order for a descriptive adjective.

If you put the adjective before the noun, it can sound more emotional, subjective, or literary:

• mi pequeño hermano = more like my dear little brother or my tiny brother

In everyday neutral Spanish, mi hermano pequeño is the usual choice.

It can mean either, depending on context.

Very often, hermano pequeño means younger brother, especially in ordinary family talk. But it can also literally suggest that he is physically small.

If you want to be more specifically about age, Spanish also uses:

• mi hermano menor = my younger brother

In everyday speech, though, mi hermano pequeño is very common.

Because adjectives in Spanish usually agree with the noun they describe in gender and number.

Here:

• hermano is masculine singular
• so the adjective must also be masculine singular
• therefore: pequeño

Compare:

• mi hermano pequeño
• mi hermana pequeña

Trabaja is the third-person singular present tense of trabajar.

The verb trabajar means to work.

Present tense forms:

• yo trabajo = I work
• tú trabajas = you work
• él / ella / usted trabaja = he / she / you work

Since mi hermano pequeño is a singular third-person subject, trabaja is the correct form.

Yes, sometimes.

The Spanish present tense can often translate into English as either:

• works
• is working

depending on context.

So Mi hermano pequeño trabaja en la ciudad usually means My little/younger brother works in the city as a general fact or habit.

If the context were about what he is doing right now, Spanish might still use trabaja, but very often it would use:

• está trabajando = is working

So this sentence most naturally sounds like a general statement.

Because Spanish often drops subject pronouns when they are not needed.

The verb ending already tells you the person:

• trabaja = he/she works

So Spanish normally says:

• Mi hermano pequeño trabaja...

rather than:

• Él trabaja...

You can add él for emphasis, contrast, or clarity, but it is not necessary here.

Because en is used for location: being or happening in a place.

• trabaja en la ciudad = he works in the city

By contrast, a is usually used for movement toward a place:

• va a la ciudad = he goes to the city

So here, since the sentence is about where he works, en is the correct preposition.

Spanish usually needs an article with nouns in cases where English might not feel it as strongly.

So:

• en la ciudad = in the city

is the natural Spanish phrasing.

Saying just en ciudad would sound incomplete or unnatural in standard Spanish.

Because la ciudad suggests a specific or understood place, or simply the city as a known environment.

• la ciudad = the city
• una ciudad = a city

With trabaja en la ciudad, the idea is usually:

• he works in the city (for example, as opposed to the countryside or suburbs), or
• he works in the city we already know about

If you said trabaja en una ciudad, it would mean he works in a city, which is less specific.

A rough Spain Spanish pronunciation would be:

• Mi hermano pequeño trabaja en la ciudad
• mee ehr-MAH-noh peh-KEH-nyoh trah-BAH-hah en lah thyoo-DHATH

A few useful points for Spain:

• pequeño: the ñ sounds like ny in canyon
• trabaja: the j is a strong throaty sound, not like English j
• ciudad: in much of Spain, the c before i sounds like th in thin
• final d in Spain is often softer than English d

So ciudad in Spain sounds roughly like thyoo-THATH or thyoo-DHATH, depending on the speaker.