Ona trzyma kubek w ręce.

That is a very common question. In Polish, the verb form already shows the person and number, so ona is often optional.

• Trzyma kubek w ręce. = She is holding a mug in her hand.
• Ona trzyma kubek w ręce. = also correct, but ona adds emphasis, contrast, or clarity.

You might include ona if:

• you want to stress that she, not someone else, is doing it
• the subject needs to be especially clear
• you are contrasting: On czyta, a ona trzyma kubek w ręce.

So the sentence with ona is correct, but in many contexts Polish would simply say Trzyma kubek w ręce.

Trzyma is the 3rd person singular present tense form of the verb trzymać.

So the pattern is:

• ja trzymam = I hold
• ty trzymasz = you hold
• on/ona/ono trzyma = he/she/it holds
• my trzymamy = we hold
• wy trzymacie = you all hold
• oni/one trzymają = they hold

In this sentence, trzyma matches ona.

Also, trzymać is usually imperfective, so it describes an ongoing state or action: holding, keeping, carrying in the hand, and so on.

It is changing by case function, but in this particular noun the accusative singular looks the same as the nominative singular.

Here, kubek is the direct object of trzyma, so it is in the accusative case.

For masculine inanimate nouns, the accusative singular is often identical to the nominative singular:

• nominative: kubek
• accusative: kubek

So even though the case is accusative, the form stays kubek.

Compare that with a feminine noun, where the form changes more visibly:

• filiżanka → filiżankę

In this sentence, ręce is in the locative case.

The preposition w can take different cases depending on meaning:

• w + locative = in, inside, at a location
• w + accusative = movement into

Here the meaning is location: the mug is in her hand, so Polish uses w + locative.

That is why you get:

• w ręce

This is the same general idea as:

• w domu = in the house
• w szkole = at school
• w torbie = in the bag

Yes. This is something learners notice very quickly.

With ręka, you will encounter both:

• w ręce
• w ręku

In everyday Polish, w ręku is extremely common in the sense of in the hand, and many speakers may find it more natural in this exact context.

So you may hear:

• Ona trzyma kubek w ręku.

Both forms are worth recognizing. If your course or textbook gives w ręce, learn it as correct, but do not be surprised if w ręku appears very often in real Polish.

Because Polish often leaves out possessive words like my, your, her, especially with body parts, when the owner is obvious from the context.

So:

• Ona trzyma kubek w ręce.

already naturally implies in her hand.

Adding jej is possible, but it is usually unnecessary unless you want emphasis or contrast:

• Ona trzyma kubek w jej ręce is not the natural way to say it in this context.
• If you really want emphasis, Polish more naturally uses something like w swojej ręce / w swoim ręku, depending on wording.

But most of the time, simple w ręce or w ręku is enough.

Not if you want the same meaning.

• w ręce / w ręku = in the hand
• ręką = with the hand / by the hand depending on context

So:

• Ona trzyma kubek w ręce. = She is holding the mug in her hand.
• Ona trzyma kubek ręką. = She is holding the mug with her hand.

The second version sounds unusual unless you are specifically emphasizing which body part she is using, because of course people normally hold things with their hands anyway.

So for the normal meaning, w ręce / w ręku is the natural choice.

No. Polish word order is more flexible than English word order.

The neutral order here is:

• Ona trzyma kubek w ręce.

But other orders are possible, depending on emphasis:

• Trzyma kubek w ręce. = neutral, without the pronoun
• Kubek trzyma w ręce. = emphasizes kubek
• W ręce trzyma kubek. = emphasizes the location
• Ona kubek trzyma w ręce. = marked, contrastive, not the most neutral

So the original sentence is a normal, straightforward order, but not the only possible one.

Polish does not have articles like English a/an and the.

So kubek can mean:

• a mug
• the mug

The exact meaning depends on context.

That is why a single Polish sentence can often be translated into English in more than one natural way. Polish relies on:

• context
• word order
• emphasis
• shared knowledge between speakers

rather than articles.

Kubek usually means a mug or a larger everyday cup, often with a handle.

It is different from:

• filiżanka = a cup, especially a teacup/coffee cup
• szklanka = a glass

So if the object is a typical ceramic mug, kubek is the natural word. English translations may vary between mug and cup, but mug is often the closer match.