Plastaffaldet er rent.

Because Danish normally writes compound nouns as a single word.

So plastaffaldet is built like this:

• plast = plastic
• affald = waste
• plastaffald = plastic waste
• plastaffaldet = the plastic waste

This is very common in Danish. Where English may write two words, Danish often makes one compound word.

-et is the definite article ending for a singular neuter noun. It corresponds to English the.

So:

• plastaffald = plastic waste
• plastaffaldet = the plastic waste

In Danish, the is often attached to the end of the noun instead of being a separate word before it.

In Danish compounds, the last part usually determines the grammatical gender.

Here, the last part is affald, and affald is neuter. That means the whole compound is also neuter:

• et affald
• et plastaffald
• plastaffaldet

So the neuter ending affects both the noun and the adjective in the sentence.

Because rent is the neuter singular form of the adjective ren.

Danish adjectives often change form depending on the noun they describe:

• ren = common gender singular
• rent = neuter singular
• rene = plural or definite attributive form

Since plastaffaldet is neuter singular, the adjective becomes rent.

That is a very common question.

After a verb like er (is), the adjective is a predicate adjective. Predicate adjectives do not use the definite -e form just because the noun is definite.

So you get:

• Plastaffaldet er rent. = The plastic waste is clean.

But when the adjective comes before the noun, it does use the definite form:

• det rene plastaffald = the clean plastic waste

So the difference is:

• before the noun: use the attributive form, often -e in definite phrases
• after er: use the predicate form, which here is rent

Er is the present tense of at være, which means to be.

So:

• jeg er = I am
• du er = you are
• han/hun er = he/she is
• de er = they are

Danish uses the same present-tense form er for all persons.

This is the normal Danish statement pattern:

• subject + verb + complement

So:

• Plastaffaldet = subject
• er = verb
• rent = complement/adjective

If you turn it into a yes/no question, Danish usually puts the verb first:

• Er plastaffaldet rent? = Is the plastic waste clean?

Yes, but it changes the feel slightly.

• Plastaffaldet er rent = the plastic waste is clean, referring to something specific
• Plastaffald er rent = plastic waste is clean / clean as a general category or substance

In real-life contexts like recycling signs, the definite form can sound natural when referring to a specific waste type being discussed.

No. Danish does not capitalize common nouns the way German does.

Plastaffaldet is capitalized here only because it is the first word of the sentence.

If it appeared in the middle of a sentence, it would normally be lowercase:

• Jeg tror, plastaffaldet er rent. = I think the plastic waste is clean.