U košarici su dvije paprike, jedan krastavac i tri kruške.

Because u means in, and when it shows a static location in Croatian, the noun usually goes into the locative case.

• dictionary form: košarica = basket
• after u for location: u košarici = in the basket

A useful contrast is:

• u košarici = in the basket
• u košaricu = into the basket

So here the items are already inside the basket, so u košarici is the correct form.

Croatian word order is more flexible than English, and the short form su often appears near the beginning of the sentence, typically in the second position.

So:

• U košarici su dvije paprike... is very natural.

This sentence structure is especially common when you first set the scene in the basket, and then say what is there.

In more English-like order, you could also say something like:

• Dvije paprike, jedan krastavac i tri kruške su u košarici.

That is grammatical, but the original version sounds more natural if the main point is what is inside the basket.

Because the sentence is talking about more than one thing: two peppers, one cucumber, and three pears.

Even though the list contains different nouns, together they make a plural subject, so Croatian uses the plural form of to be:

• su = are

If there were just one item, you would use je instead:

• U košarici je jedna paprika.

Because Croatian numbers change for gender.

• paprika is feminine, so two becomes dvije
• krastavac is masculine, so one becomes jedan

Compare:

• jedna paprika = one pepper
• jedan krastavac = one cucumber
• jedna kruška = one pear
• dvije paprike = two peppers

So the numeral has to agree with the gender of the noun, especially with jedan/jedna/jedno and dva/dvije.

Because dvije is the feminine form of two.

Use:

• dva with masculine and neuter nouns
• dvije with feminine nouns

Examples:

• dva krastavca = two cucumbers
• dva sela = two villages
• dvije paprike = two peppers
• dvije kruške = two pears

Since paprika is feminine, dvije is the correct choice.

After the numbers 2, 3, and 4, Croatian nouns use a special counting form. In traditional grammar, this is often described as a form based on the genitive singular.

So:

• dvije paprike
• tri kruške

For many feminine nouns, this form looks the same as the nominative plural, which is why it can seem confusing.

A very important comparison is:

• jedna paprika
• dvije paprike
• tri paprike
• četiri paprike
• pet paprika

Notice that after 5 and above, the pattern changes again.

Because after jedan, the noun behaves normally and stays in the nominative singular.

So:

• jedan krastavac = one cucumber

But after dva, tri, četiri, the noun changes into the counting form:

• dva krastavca
• tri krastavca
• četiri krastavca

So jedan is different from 2, 3, 4 in this respect.

Yes, sometimes you can, depending on style and context.

You could say:

• U košarici su dvije paprike, krastavac i tri kruške.

That would still be understandable. But using jedan is very natural here because it matches the numbered list:

• two peppers
• one cucumber
• three pears

So jedan makes the sentence more balanced and explicit.

Yes. Croatian word order is fairly flexible, although some versions sound more natural than others depending on what you want to emphasize.

The original:

• U košarici su dvije paprike, jedan krastavac i tri kruške.

This emphasizes the location first: in the basket.

You could also say:

• Dvije paprike, jedan krastavac i tri kruške su u košarici.

This puts the list first and the location later.

Both are grammatical, but the original sentence is very natural if you are answering a question like What is in the basket?

Yes, in everyday Croatian you may also hear ima used in a there is / there are sense.

For example:

• U košarici ima dvije paprike, jedan krastavac i tri kruške.

That is common in speech. But U košarici su... is also perfectly normal and very clear.

A simple way to think about the difference:

• su focuses on the items as the subject of the sentence
• ima is more like English there is / there are

Both patterns are useful to learn.

After 5 and higher, Croatian changes the noun form again.

So tri kruške becomes:

• pet krušaka = five pears

Compare:

• dvije paprike
• tri kruške
• četiri jabuke
• pet krušaka

With larger numbers, the noun usually takes the genitive plural.

So a sentence like this could become:

• U košarici je pet krušaka.

That is a very useful pattern to learn early:

• 2, 3, 4 = one counting pattern
• 5+ = another counting pattern