changmuneul yeon chaero jamyeon mogihante mulligi swiwo.

-ㄴ/은 채로 means in the state of having done X, or while leaving X as it is.

So 연 채로 comes from 열다 and means with it left open. It focuses on the continued state, not just the action of opening.

In this sentence, it tells you that the window stays open while you sleep.

연 is the adnominal form of 열다 used before 채로.

A helpful way to think of it:

• 채 behaves like a noun meaning something like state
• so the verb before it has to appear in a form that can modify a noun

That is why you get:

• 열다 → 연 채로

Compare:

• 창문을 열고 자다 = open the window and sleep
• 창문을 연 채로 자다 = sleep with the window left open

Both can be natural, but 연 채로 more clearly emphasizes the unchanged open state.

Because 열다 is a transitive verb, and 창문 is its direct object.

So:

• 창문을 열다 = to open the window

If you used 창문이, it would change the structure and meaning. Here, the speaker is talking about the action of opening the window, so 을 is the normal particle.

자면 is:

• 자다 = to sleep
• -면 = if / when

So 자면 means if you sleep or when you sleep.

In Korean, the subject is often omitted when it is understood from context. Here it has a general meaning, like if you sleep or if someone sleeps in that situation.

한테 marks the thing doing the action to you in this passive-type expression.

So:

• 모기한테 물리다 = to get bitten by a mosquito

A few notes:

• 한테 is common and conversational
• 에게 is more formal
• with 물리다, you will also very often hear 모기에 물리다

So these are all possible depending on style:

• 모기한테 물리다
• 모기에게 물리다
• 모기에 물리다

In everyday speech, 한테 sounds very natural.

Because 물리다 is the passive form of 물다.

• 물다 = to bite
• 물리다 = to be bitten

In this sentence, the sleeper is not doing the biting. The sleeper is the one receiving the action. So Korean uses the passive:

• 모기한테 물리다 = to get bitten by mosquitoes

If you said 물기 쉬워, it would sound like easy to bite, which is the wrong direction of action here.

-기 쉽다 literally means to be easy to do, but in many real sentences it often means to be likely to happen, to be prone to, or to be susceptible to.

So here:

• 물리기 쉬워 does not just mean some abstract literal ease
• it means you are likely to get bitten or you are prone to getting bitten

This is a very common Korean pattern:

• 실수하기 쉬워 = prone to making mistakes
• 감기에 걸리기 쉬워 = likely to catch a cold
• 잊기 쉬워 = easy to forget / prone to forgetting

Yes. Korean often leaves out the subject when it is obvious or general.

Here, the hidden subject is something like:

• you
• someone
• people in general

So the sentence has a general warning-like feel. It is not necessarily talking about one specific person unless the context makes that clear.

쉬워 is the casual, non-polite form.

The levels are:

• 쉽다 = dictionary form
• 쉬워요 = polite everyday form
• 쉬워 = casual plain form

So the sentence is in a casual speaking style. If you wanted to say the same thing politely, you could say:

• 창문을 연 채로 자면 모기한테 물리기 쉬워요.

Yes, you can, and it would sound natural in many situations.

But there is a nuance difference:

• 창문을 열고 자면 = if you open the window and sleep
• 창문을 연 채로 자면 = if you sleep with the window left open

The first one focuses more on the sequence of actions. The second one focuses more on the continued state during sleep.

In this sentence, 연 채로 is a very good choice because the important point is that the window remains open the whole time.