Termostat je v pokoji.

Because the preposition v meaning in requires the locative case when it describes location.

• basic dictionary form: pokoj = room
• after v for location: v pokoji = in the room

So in this sentence:

• Termostat = subject
• je = is
• v pokoji = in the room

This is a very common pattern in Czech:

• v domě = in the house
• v autě = in the car
• v pokoji = in the room

Je means is. It is the 3rd person singular present form of the verb být = to be.

So:

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

In Termostat je v pokoji, je links the subject Termostat with the location v pokoji, just like English is.

Czech does not have articles like a, an, or the.

So Termostat je v pokoji can mean:

• The thermostat is in the room
• A thermostat is in the room

Which one is meant depends on context. In real use, the listener usually understands from the situation what is meant.

Termostat is a masculine inanimate noun.

That matters for things like adjectives and past tense forms later on. In this sentence, though, you mainly just need to recognize that Termostat is in the nominative singular because it is the subject.

Yes. Czech word order is more flexible than English.

Both are correct:

• Termostat je v pokoji.
• V pokoji je termostat.

The difference is mostly one of emphasis:

• Termostat je v pokoji. → focuses more naturally on the thermostat
• V pokoji je termostat. → starts with in the room, so the location is more prominent

English usually has stricter word order, but Czech can move parts around more freely.

A simple learner-friendly pronunciation guide is:

ter-mo-stat ye f po-ko-yi

A few key points:

• j in Czech is pronounced like English y in yes
• je sounds like ye
• v is often pronounced like f before a voiceless consonant such as p, so v pokoji often sounds like f pokoji
• r is rolled or tapped more than in English

So the whole sentence is approximately:

TER-mo-stat ye f PO-ko-yi

The basic preposition is v. A longer form ve is used only when pronunciation would be awkward.

Here, v pokoji is easy to say, so Czech uses v.

You will see ve in phrases like:

• ve škole = at school
• ve městě = in the city

So you do not use ve everywhere—only when it sounds better or is standard usage.

When v means in and describes a location, yes, it normally takes the locative:

• v pokoji = in the room
• v domě = in the house
• v Praze = in Prague

For this sentence, the important rule is simple:

• Where is it? → v
  • locative

The basic dictionary form is pokoj.

Its forms here are:

• pokoj = nominative singular, the base form
• v pokoji = locative singular after v

So if you look this word up in a dictionary, you would search for pokoj, not pokoji.

Normally, no. In standard Czech, in the present tense, the verb to be is usually stated in sentences like this.

So you say:

• Termostat je v pokoji.

not normally:

• Termostat v pokoji.

Czech sometimes omits je in special styles like headlines, notes, or very informal compressed speech, but for normal learners' Czech, keep je.

Yes, it is a completely natural and correct sentence.

It is a straightforward location sentence:

• Termostat = what we are talking about
• je = is
• v pokoji = where it is

It is a good model for many similar sentences, such as:

• Stůl je v kuchyni. = The table is in the kitchen.
• Kniha je v tašce. = The book is in the bag.
• Pes je na zahradě. = The dog is in the garden.

So it is a useful pattern to learn early.