Baloni su u stanu.

Baloni means balloons. It is the plural nominative form of balon (balloon).

The ending -i is a very common masculine plural ending in Serbian:

• balon = balloon
• baloni = balloons

In this sentence, baloni is the subject, so the nominative plural is used.

Su is the 3rd person plural form of the verb biti (to be) in the present tense.

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is
• mi smo = we are
• vi ste = you are
• oni/one/ona su = they are

Since baloni is plural (balloons), Serbian uses su = are.

Because after u meaning in, Serbian normally uses the locative case when talking about location.

So:

• stan = apartment/flat
• u stanu = in the apartment

This is a very important pattern:

• u + locative = in/at a place
• u + accusative = into/to a place, when there is movement

Compare:

• Baloni su u stanu. = The balloons are in the apartment.
• Stavljam balone u stan. = I am putting the balloons into the apartment.

Stanu is the locative singular of stan.

The noun stan is masculine, and in the singular locative it becomes:

• stan → stanu

So in u stanu, the preposition u requires the locative here because the sentence describes where something is.

Not exactly. Stan usually means apartment or flat, not a house.

A house is usually:

• kuća = house

So:

• u stanu = in the apartment / flat
• u kući = in the house

That distinction is useful because English learners may want to translate home or house too broadly.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Baloni su u stanu.

But you may also hear:

• U stanu su baloni.
• Baloni u stanu su. (much less neutral, more marked or poetic)

The most natural choice in everyday speech is usually:

• Baloni su u stanu.

If you move u stanu to the front, it often gives more emphasis to the location:

• U stanu su baloni. = It is in the apartment that the balloons are.

Normally, in a full standard sentence like this, no. Serbian requires the present-tense form of to be here:

• Baloni su u stanu.

Leaving it out:

• Baloni u stanu.

would sound incomplete in standard Serbian, unless it is being used as a note, a headline, or some very shortened casual expression.

So for normal sentence-building, keep su.

Serbian does not have articles like English a/an/the.

So baloni can mean:

• balloons
• the balloons

And u stanu can mean:

• in an apartment
• in the apartment

The exact meaning depends on context.

That is why one Serbian sentence can correspond to more than one English translation.

The dictionary form is balon, and it is a masculine noun. Many masculine nouns in Serbian end in a consonant in the singular:

• balon
• stan
• grad
• pas

Then many of them form the nominative plural in -i:

• baloni
• stanovi
• gradovi
• psi (irregular pattern compared with the others)

So seeing balon helps you identify the gender and understand why the plural form is baloni.

Yes, very naturally.

Even though Serbian literally says Balloons are in the apartment, in English the best translation in many situations may be:

• There are balloons in the apartment.

Serbian often uses a normal subject + biti + location structure where English may prefer there is/there are.

So depending on context, either of these could be a good translation:

• The balloons are in the apartment.
• There are balloons in the apartment.

The singular version would be:

• Balon je u stanu. = The balloon is in the apartment.

Compare:

• balon = balloon
• baloni = balloons
• je = is
• su = are

So the sentence changes like this:

• Balon je u stanu.
• Baloni su u stanu.