De verkoudheid duurt lang.

Because verkoudheid is a de-word in Dutch. Unfortunately, for many nouns, you simply have to learn whether they take de or het.

A useful clue here is the ending -heid. Nouns ending in -heid are virtually always de-words:

• de vrijheid = freedom
• de mogelijkheid = possibility
• de verkoudheid = a cold / the cold

So if you see a noun ending in -heid, you can safely expect de.

Yes. Verkoudheid is closely related to verkouden, which means to have a cold or cold-like / suffering from a cold, depending on context.

The noun is built from that idea plus the suffix -heid, which often turns something into an abstract noun, similar to English -ness in some cases.

So:

• verkouden zijn = to have a cold
• de verkoudheid = the cold / the illness

Dutch often uses both patterns:

• Ik ben verkouden. = I have a cold.
• Ik heb een verkoudheid. = I have a cold.

The first one is usually more common in everyday speech.

Because the subject is singular: de verkoudheid.

The infinitive is duren = to last.
In the present tense, with a third-person singular subject, Dutch adds -t:

• ik duur (rare in practice, because this verb is not often used with *ik in ordinary situations)*
• jij duurt / u duurt
• hij/zij/het duurt
• de verkoudheid duurt

So duurt is the correct present-tense form for a singular subject.

Duren means to last or to continue for a certain amount of time.

In this sentence, it means the cold is lasting a long time.

Examples:

• De film duurt twee uur. = The film lasts two hours.
• De vergadering duurt lang. = The meeting lasts a long time.
• De verkoudheid duurt lang. = The cold lasts a long time.

So Dutch uses duren much like English to last.

Because lang is not being used directly before a noun here. It is used after the verb duurt and functions more like an adverbial complement: it tells you how long something lasts.

Compare:

• een lange dag = a long day
  
  • here lange is an adjective before a noun
• De dag duurt lang. = The day lasts a long time
  
  • here lang stays plain, without -e

So in De verkoudheid duurt lang, lang is correct.

Yes, this is very normal Dutch word order for a simple main clause:

• De verkoudheid = subject
• duurt = finite verb
• lang = complement/adverbial

So the structure is basically:

Subject + verb + rest

That is the standard order in Dutch main clauses.

It is grammatical and natural, but in real conversation Dutch speakers might often make it more personal or more specific, for example:

• Mijn verkoudheid duurt lang. = My cold is lasting a long time.
• Deze verkoudheid duurt lang. = This cold is lasting a long time.
• Ik ben al lang verkouden. = I’ve had a cold for a long time.

So the sentence is fine, but depending on context, speakers may prefer a version that sounds more directly connected to the situation.

Yes, and very often that is the more everyday way to express it.

Compare:

• Ik ben verkouden. = I have a cold.
• De verkoudheid duurt lang. = The cold lasts a long time.

If you want to talk about the illness itself as a noun, verkoudheid is useful. If you want to describe your condition, verkouden zijn is often more natural.

For example:

• Ik ben al een week verkouden. = I’ve had a cold for a week already.
• Mijn verkoudheid duurt al een week. = My cold has already lasted a week.

Both are correct, but the first often sounds more conversational.

Roughly, it sounds like:

ver-KOUT-hite

A few notes:

• ver- is unstressed
• koud sounds a bit like English cowd, but with a Dutch ou
• heid sounds somewhat like hite, not like English hide

The stress is on koud:

ver-KOUD-heid

If pronunciation is important, it helps to listen to native audio, because the Dutch diphthongs in koud and heid are not exactly the same as English vowel sounds.

Yes. In many contexts, lang duren can be translated as either to last a long time or to take a long time, depending on what sounds natural in English.

For example:

• Het duurt lang. = It takes a long time.
• De les duurt lang. = The lesson lasts a long time.
• De verkoudheid duurt lang. = The cold lasts a long time.

So the Dutch verb stays the same, while English may choose different wording depending on the subject.