El radi està trencat.

• El = the (masculine singular definite article)
• radi = the noun
• està = is from estar
• trencat = broken

So the structure is:

article + noun + estar + adjective/past participle

Because radi is a masculine singular noun in Catalan, so it takes el.

A few matching patterns:

• el radi = the spoke / the radius
• la roda = the wheel
• els radis = the spokes
• les rodes = the wheels

The article has to match the noun in gender and number.

Catalan often distinguishes between ser and estar, somewhat like Spanish.

Here, està trencat means is broken as a state or condition. It suggests the thing is in a broken condition, often as the result of something happening.

So:

• està trencat = it is broken
• és trencat would sound unnatural in this context

For physical conditions like broken, open, closed, dirty, ready, Catalan very often uses estar.

Trencat is the past participle of trencar (to break), but in this sentence it works like an adjective meaning broken.

You can think of it as:

• trencar = to break
• trencat = broken

Because it is being used adjectivally, it agrees with the noun:

• el radi està trencat = the spoke is broken
• la barra està trencada = the bar is broken
• els radis estan trencats = the spokes are broken
• les barres estan trencades = the bars are broken

That is the regular masculine singular past participle ending for many -ar verbs in Catalan.

Examples:

• trencar → trencat
• tancar → tancat
• obrir → obert (this one is irregular)
• fer → fet (irregular)

In your sentence, trencat matches radi, which is masculine singular.

The adjective and often the article would change to match.

Examples:

• La roda està trencada. = The wheel is broken.
• Els radis estan trencats. = The spokes are broken.
• Les peces estan trencades. = The pieces are broken.

Notice two things change:

1. the article
2. the form of trencat

And in the plural, the verb changes too:

• està = is
• estan = are

Yes. Radi can have more than one meaning depending on context, including:

• spoke of a wheel
• radius

So El radi està trencat could mean different things depending on the context already given to the learner.

Catalan relies on context here, just as English sometimes does.

Normally, no. In an ordinary sentence, Catalan usually wants the definite article here:

• El radi està trencat.

Without the article, it sounds incomplete or unnatural in most normal contexts, unless you are using a very special style such as labels, notes, or headlines.

A rough pronunciation guide is:

el RAH-di es-TAH tren-KAT

A few notes:

• està has the stress on the last syllable: -tà
• trencat has the stress on the last syllable: -cat
• The exact sound of r and some vowels varies by dialect

If you want to sound natural, the main thing is to stress:

• està
• trencat

correctly.

Yes, but El radi està trencat is the normal, neutral order.

Catalan can change word order for emphasis, for example in speech:

• Està trencat, el radi.

That sounds more marked or emphatic, something like The spoke is broken with extra focus.

For a learner, the safest standard pattern is:

Subject + estar + adjective

You make it negative by putting no before the verb:

• El radi no està trencat. = The spoke is not broken.

This is the standard way to negate the sentence in Catalan.

In everyday Catalan, intonation often does the job:

• El radi està trencat? = Is the spoke broken?

You can also write it with question marks in normal spelling:

• El radi està trencat?

Catalan does not usually need a separate equivalent of English do or inversion like Is the spoke.... The same word order can remain, and the rising intonation signals the question.