U hodniku su cveće i poklon.

Because after u when it means in / inside, Serbian uses the locative case.

• hodnik = hallway, corridor
• u hodniku = in the hallway

So here:

• u = in
• hodniku = locative singular of hodnik

This is different from u hodnik, which would use the accusative and usually mean motion into the hallway, not location.

So:

• U hodniku = in the hallway
• U hodnik = into the hallway

Because the sentence has two things being talked about:

• cveće = flowers
• poklon = gift

Together they form a compound subject, so the verb is plural:

• su = are

Even though poklon is singular and cveće also looks singular grammatically, the whole phrase cveće i poklon means flowers and a gift, so Serbian uses plural agreement.

That is why:

• U hodniku su cveće i poklon. = There are flowers and a gift in the hallway.

Because cveće is a collective noun in Serbian. Grammatically, it is usually treated as singular neuter, even though in meaning it refers to multiple flowers.

This is a very common point of confusion for English speakers.

Compare:

• cvet = a flower
• cvetovi = flowers (countable plural)
• cveće = flowers / floral stuff / a mass or collective of flowers

So cveće often behaves like a singular noun in grammar, but its meaning can be plural in English.

In this sentence, however, the verb is plural not because cveće itself is plural, but because it is joined with another noun:

• cveće i poklon = flowers and a gift

They are in the nominative case, because they are the subject of the sentence.

• cveće = nominative
• poklon = nominative

The structure is basically:

• U hodniku = in the hallway
• su = are
• cveće i poklon = flowers and a gift

So the things that are in the hallway stay in the nominative.

This is normal Serbian word order. Serbian word order is much more flexible than English word order.

The sentence starts with the location:

• U hodniku = in the hallway

Then comes the verb:

• su = are

Then the things being introduced:

• cveće i poklon = flowers and a gift

This word order sounds natural when you are saying what is located somewhere, especially when introducing new information.

A very literal English-like structure would feel less natural in many contexts. Serbian often prefers something like:

• U hodniku su cveće i poklon.

rather than forcing the subject to come first.

Yes, very much.

Serbian often does not need a separate word like English there in sentences of existence or location.

So:

• U hodniku su cveće i poklon.

is naturally understood as:

• There are flowers and a gift in the hallway.

Serbian simply uses the normal verb biti (to be) without adding a dummy subject like English there.

Yes. Serbian allows several word orders, but they can sound slightly different in emphasis.

For example:

• U hodniku su cveće i poklon.
• Cveće i poklon su u hodniku.

Both are grammatical.

The difference is mostly about focus:

• U hodniku su cveće i poklon. emphasizes the location first, then tells you what is there.
• Cveće i poklon su u hodniku. starts with the things, then tells you where they are.

So the original sentence is especially natural if the hallway is the starting point of the statement.

Because hodnik is understood as an enclosed space, so Serbian normally uses u for being in it.

• u hodniku = in the hallway

In Serbian, na is used for many surfaces and some locations, but not normally for hodnik in the basic sense.

So for a learner, the natural expression to remember is:

• u sobi = in the room
• u kući = in the house
• u hodniku = in the hallway

Yes, but it would not mean exactly the same thing in tone.

• cvetovi = flowers as individual countable flowers
• cveće = flowers as a collective or general mass

So:

• U hodniku su cveće i poklon.

sounds natural if you mean something like flowers and a gift are in the hallway in a general sense.

If you said:

• U hodniku su cvetovi i poklon.

that would sound more like you are talking about specific individual flowers. In many everyday situations, cveće is the more natural choice.

Yes. Poklon is a masculine noun.

• singular nominative: poklon
• meaning: gift / present

In this sentence it stays in its dictionary form because it is the subject:

• poklon = a gift

That is why you see:

• cveće i poklon

with both nouns in the nominative.