Prostředí je klidné.

Because klidné agrees with prostředí, which is a neuter singular noun.

Czech adjectives change their endings to match the noun’s:

• klidný = masculine
• klidná = feminine
• klidné = neuter

So in Prostředí je klidné, the neuter ending -é is the correct one.

It is singular here.

A learner might expect a different ending for a singular noun, but prostředí is a neuter singular noun. In this sentence, you can also tell it is singular because it goes with je (is), not jsou (are).

It is in the nominative case, because it is the subject of the sentence.

In other words:

• prostředí = the thing being described
• je klidné = is calm/quiet

So prostředí is the subject, and subjects are normally in the nominative.

It is also in the nominative.

After the verb být (to be), Czech usually uses a predicate adjective in the nominative:

• Město je krásné.
• Dítě je malé.
• Prostředí je klidné.

So klidné is nominative singular neuter, matching prostředí.

Je means is. It is the 3rd person singular form of být (to be).

So:

• já jsem = I am
• ty jsi = you are
• on/ona/ono je = he/she/it is

In this sentence, prostředí je klidné literally means The environment/setting is calm.

Normally, no.

In standard Czech, the present-tense form of být is usually not omitted in normal sentences. So:

• correct: Prostředí je klidné.
• not normal in standard speech: Prostředí klidné.

You might see omission in headlines, notes, or very stylized language, but for regular learning, keep je.

No. Czech does not have articles like a, an, or the.

So prostředí can mean:

• the environment
• an environment
• the setting
• the surroundings

The exact meaning depends on context, not on an article.

Yes, Czech word order is fairly flexible, but Prostředí je klidné is the most neutral order.

This version simply states the fact:

• Prostředí je klidné. = neutral, natural

Other orders are possible, but they usually sound more marked or emphasize something:

• Klidné je prostředí. = emphasis on klidné
• Je klidné prostředí. = possible only in special contexts, not the normal basic version

So for a learner, Prostředí je klidné is the safest choice.

The stress is on the first syllable, as usual in Czech: PROS-tře-dí.

The hardest part for many learners is ř in prostředí. It is a special Czech sound, something like a mix of r and zh. If you cannot say it yet, an approximate r is better than getting stuck.

A rough learner-friendly guide:

• pros = like pross
• tře = with the Czech ř
• dí = long dee

Also, the final í is long.

It can mean either, depending on context.

With prostředí, common English translations are:

• The environment is calm.
• The setting is peaceful.
• The surroundings are quiet.

If you want to emphasize low noise, Czech often uses tiché (quiet in the sound sense).
If you want to emphasize peaceful, not stressful, klidné is very natural.

It is neutral standard Czech.

It sounds natural in everyday language, writing, descriptions, reviews, and formal contexts too. It is not slang, and it is not especially literary. That makes it a very useful model sentence for learners.