Na ljuljački je hrabrija nego na klackalici.

Croatian often leaves out subject pronouns when they are clear from context. The sentence does not need ona (she) because the predicate already suggests a feminine singular subject:

• hrabrija = feminine singular
• je = is

So the subject is understood as she (or another feminine singular noun already known from context).

Because of hrabrija.

Croatian adjectives agree with the noun they describe in gender, number, and case when needed. Here the adjective is used predicatively, and the form hrabrija is the feminine singular comparative form.

Compare:

• hrabriji = masculine singular
• hrabrija = feminine singular
• hrabrije = neuter singular / adverbial form in some contexts

So this sentence is talking about a feminine singular subject.

Because this is an adjective describing a person, not an adverb.

• hrabrija = braver (feminine singular adjective)
• hrabrije = more bravely (adverb), or a neuter adjective form in other contexts

Here the meaning is she is braver, not she behaves more bravely, so the adjective form hrabrija is the correct choice.

The basic dictionary form is hrabar = brave.

Its comparative is:

• masculine: hrabriji
• feminine: hrabrija
• neuter: hrabrije

So hrabrija means braver for a feminine singular subject.

They are in the locative singular.

That is because they follow na in a location meaning:

• na ljuljački = on the swing
• na klackalici = on the seesaw

With na, Croatian commonly uses:

• accusative for motion toward something
• locative for being at/on something

Here the meaning is location, not movement, so the locative is used.

Because na is the normal preposition for being on something like playground equipment.

So:

• na ljuljački = on the swing
• na klackalici = on the seesaw

This is a literal physical on.

Because each place phrase needs its own preposition.

Croatian does not drop it here. The comparison is between two full prepositional phrases:

• na ljuljački
• na klackalici

So nego na klackalici is the natural structure. Without na, the sentence would be ungrammatical.

Nego is the natural comparative connector here because the sentence compares two situations/locations:

• na ljuljački
• na klackalici

Croatian often uses:

• od + genitive when comparing with a noun or pronoun
  
  • Ana je hrabrija od Marka.
• nego when comparing with another phrase or clause
  
  • hrabrija je na ljuljački nego na klackalici

So in this sentence, nego is the right choice.

Because je is a clitic, and Croatian clitics usually go in the second position of the sentence or clause.

Here the first unit is Na ljuljački, so je comes right after it:

• Na ljuljački je hrabrija nego na klackalici.

This may feel unusual to an English speaker, but it is very normal in Croatian.

Yes, Croatian word order is flexible, though not completely free.

For example, you could also say:

• Hrabrija je na ljuljački nego na klackalici.
• Ona je hrabrija na ljuljački nego na klackalici.

The original version puts extra focus on Na ljuljački at the beginning. That makes the location sound especially prominent.

They are:

• ljuljačka = swing
• klackalica = seesaw

Both are feminine nouns. In this sentence they appear in locative singular:

• ljuljačka → na ljuljački
• klackalica → na klackalici

Yes, you could.

• Ona je hrabrija na ljuljački nego na klackalici.

That is grammatical, but Croatian often omits ona unless you want emphasis, contrast, or extra clarity. The version without ona sounds very natural.