i uijaneun pyeonhage anjeul su isseoyo.

Yes:

• 이 = this
• 의자 = chair
• -는 = topic marker
• 편하게 = comfortably / in a comfortable way
• 앉을 수 있어요 = can sit / are able to sit

So the structure is basically:

As for this chair, you can sit comfortably.

A very natural English rendering is often something like This chair is comfortable to sit on/in.

의자는 is 의자 + 는.

The particle -는 marks 의자 as the topic of the sentence. It gives the sense of as for this chair... and then the speaker says something about it.

So:

• 이 의자는 = as for this chair
• 이 의자 by itself = just this chair

In real conversation, Korean often uses topic markers when introducing or commenting on something. Here, the speaker is making a statement about the chair.

Great question. Both can sometimes translate similarly, but they feel different.

• 이 의자는 focuses on this chair as the topic
• 이 의자가 would focus more on this chair as the subject, often with a contrastive or identifying feel

With -는, the sentence sounds like:

• As for this chair, it’s possible to sit comfortably.

With -가, it can sound more like:

• This chair is the one that you can sit on comfortably.

So -는 is very natural if you are simply commenting on the chair.

편하게 is the adverb form of 편하다.

• 편하다 = to be comfortable
• 편하게 = comfortably

It uses the ending -게, which turns an adjective into an adverb.

Here, 편하게 modifies the verb 앉다 (to sit), so it means sit comfortably.

Compare:

• 편한 의자 = a comfortable chair
  
  • here 편한 modifies the noun 의자
• 편하게 앉다 = to sit comfortably
  
  • here 편하게 modifies the verb 앉다

So 편하게 is used because the sentence is talking about how you sit, not directly describing the chair with an adjective.

앉을 수 있어요 is the common Korean pattern for can sit or be able to sit.

The grammar is:

• verb stem + -(으)ㄹ 수 있다

Here:

• 앉다 = to sit
• verb stem = 앉-
• since the stem ends in a consonant, you use -을
• so: 앉을 수 있다
• polite form: 앉을 수 있어요

So the full idea is to be able to sit or it is possible to sit.

Some similar examples:

• 먹을 수 있어요 = can eat
• 볼 수 있어요 = can see
• 갈 수 있어요 = can go

In this sentence, it usually means the chair allows comfortable sitting.

So the focus is less about someone's physical ability and more about the chair’s suitability or comfort.

That is why a natural English meaning is often:

• This chair is comfortable to sit on/in
• You can sit comfortably in this chair

If you said this while testing furniture, people would understand it as a comment about the chair, not about your personal skill of sitting.

Yes, 편히 is also possible.

Both 편히 and 편하게 can mean comfortably. In everyday speech, 편하게 is extremely common and often feels a bit more conversational and natural in many contexts.

So:

• 편하게 앉을 수 있어요
• 편히 앉을 수 있어요

Both are grammatical.

That said, 편하게 is probably the form many learners will hear more often in casual spoken Korean.

Yes, but the nuance changes.

Without 이:

• 의자는 편하게 앉을 수 있어요
• This can mean chairs or the chair depending on context, but you lose the specific this chair meaning.

Without -는, Korean often sounds less complete unless another particle is used, though casual speech sometimes drops particles:

• 이 의자 편하게 앉을 수 있어요
  
  • possible in conversation, but more colloquial
• 이 의자에 편하게 앉을 수 있어요
  
  • adds 에, making the location/target clearer: You can sit comfortably in/on this chair

So 이 의자는 is a neat, standard way to frame the sentence.

있어요 is in the polite informal style, often called 해요체. It is very common in everyday Korean and appropriate in many normal situations.

Related levels:

• 앉을 수 있어요 = polite, everyday
• 앉을 수 있습니다 = more formal
• 앉을 수 있어 = casual, plain spoken style

So this sentence is polite and natural for regular conversation.

앉을 is pronounced roughly like 안즐.

This happens because of Korean sound rules:

• the word is spelled 앉을
• in pronunciation, it becomes [안즐]

So the whole sentence sounds approximately like:

• 이 의자는 편하게 안즐 수 이써요

That is only a rough guide in English spelling, but it may help you recognize it when listening.