Hi ha plàtans a la cuina? Sí, n'hi ha dos sobre la taula.

Hi ha is the standard Catalan way to express existence: there is / there are. It comes from the verb haver-hi, and in the present tense it stays hi ha whether the noun is singular or plural.

So:

• Hi ha un plàtan. = There is a banana.
• Hi ha plàtans. = There are bananas.

In standard Catalan, you do not say hi han here.

Because Catalan often uses a bare plural after hi ha, especially in questions and general statements.

So Hi ha plàtans a la cuina? means Are there any bananas in the kitchen?

This is similar to English using any or some, even though Catalan does not need a separate word here.

N' is the shortened form of the weak pronoun en. Here it replaces the noun plàtans so you do not have to repeat it.

So:

• Sí, n'hi ha dos. = Yes, there are two of them.
• More literally: Yes, of them there are two.

This kind of pronoun is very common in Catalan when talking about quantities.

Because they are doing different jobs.

• hi is part of the existential expression haver-hi = there is / there are
• n' replaces the noun already mentioned, here plàtans

So n'hi ha dos means something like there are two of them.

A useful way to think about it is:

• hi ha = there is / there are
• n'hi ha dos = there are two of them

Yes. That is completely correct.

The difference is:

• Sí, hi ha dos plàtans sobre la taula. repeats the noun
• Sí, n'hi ha dos sobre la taula. avoids repeating it

Since plàtans was already mentioned in the question, the version with n' is very natural.

If you leave out the noun, Catalan normally wants that pronoun:

• natural: N'hi ha dos
• not natural: Hi ha dos (unless the noun is stated right after it)

Because plàtans is a masculine noun.

In Catalan, the number two has gender:

• dos for masculine nouns
• dues for feminine nouns

So:

• dos plàtans
• dues pomes

In Catalan, a can mean to, but it is also very commonly used for location, especially with places and rooms.

So a la cuina means in the kitchen or at the kitchen, depending on English wording.

This is normal Catalan:

• a casa = at home
• a l'escola = at school
• a la cuina = in the kitchen

English separates to / in / at more strictly than Catalan does.

Here sobre la taula means on the table.

The preposition sobre can mean on, over, or above, depending on context. In this sentence, the meaning is clearly physical position: the bananas are on the table.

You may also hear damunt de la taula, which also means on top of the table.

The accent distinguishes sí meaning yes from si meaning if.

So:

• sí = yes
• si = if

The accent helps show that these are different words.

Because the weak pronoun en becomes n' before a vowel or mute h.

So:

• en + hi ha becomes n'hi ha

This is just the normal written form. It is the same pronoun, only shortened because of the sound that follows.