Термометр лежить біля тонометра.

Because біля requires the genitive case in Ukrainian.

The dictionary form is тонометр. After біля, it changes to тонометра.

So:

• тонометр = nominative singular
• біля тонометра = near the blood pressure monitor

This is a very common pattern: many prepositions in Ukrainian require a specific case.

Термометр is in the nominative case, which is the usual case for the subject.

Meanwhile, тонометра is in the genitive case because it follows біля.

So the structure is:

• термометр = the thing being talked about
• лежить = lies / is lying
• біля тонометра = near the blood pressure monitor

In other words, the thermometer is the thing located somewhere.

Лежить literally means lies or is lying.

For objects, Ukrainian often uses verbs like:

• лежати = to lie
• стояти = to stand
• висіти = to hang

So Термометр лежить біля тонометра sounds natural if the thermometer is physically lying there, probably on a surface.

In English, we often just say is, but Ukrainian often prefers a more specific position verb.

Usually, yes. Лежати suggests that something is in a lying position, often resting flat or horizontally.

So this sentence gives a little extra physical information:

• not just that the thermometer is near the blood pressure monitor
• but that it is lying there

If you only wanted to express location more neutrally, you might hear знаходиться, but лежить is more natural for many everyday situations involving objects on a table, shelf, bed, etc.

The basic form is лежати, meaning to lie.

Лежить is:

• present tense
• 3rd person singular

So it means:

• he/she/it lies
• or more naturally here, it is lying

Because термометр is singular, the verb is singular too.

Ukrainian has no articles.

So:

• термометр can mean a thermometer or the thermometer
• тонометра can mean of a blood pressure monitor or of the blood pressure monitor, depending on context

English requires articles, but Ukrainian does not. The meaning is understood from the situation or from the wider context.

Grammatically, є can mean is, but in sentences like this, Ukrainian usually does not use є the way English uses is.

Also, this sentence already has the verb лежить, which is more specific and natural.

So:

• Термометр лежить біля тонометра = natural
• Термометр є біля тонометра = unnatural in normal everyday usage

If you want a neutral verb of location, знаходиться is possible, but it often sounds more formal:

• Термометр знаходиться біля тонометра

Yes. Ukrainian word order is fairly flexible.

You can also say:

• Біля тонометра лежить термометр.

This still means the same basic thing, but the emphasis changes a little.

• Термометр лежить біля тонометра focuses first on the thermometer
• Біля тонометра лежить термометр focuses first on the location

So the original sentence is neutral and natural, but other orders are possible.

No. Ukrainian has a few options.

For example:

• біля = near, by
• коло = near, by
• поруч із = next to, beside

But they do not all behave exactly the same way.

For example:

• біля тонометра
• коло тонометра

Both use the genitive.

But:

• поруч із тонометром

Here із requires the instrumental case, so тонометр becomes тонометром.

Usually біля means near / by / beside, but not necessarily touching.

So Термометр лежить біля тонометра suggests the thermometer is close to the blood pressure monitor, but it does not guarantee that they are right up against each other.

If you want to stress right next to, поруч із is often a stronger choice:

• Термометр лежить поруч із тонометром.

Yes. Both are masculine singular inanimate nouns.

You can tell from their dictionary forms:

• термометр
• тонометр

In the sentence:

• термометр stays in nominative singular
• тонометра is genitive singular

This is why the genitive ending is -а here, which is common for masculine inanimate nouns.