naengjanggo-e sagwaga isseoyo.

에 marks a location in sentences with 있다 and 없다.

So in 냉장고에 사과가 있어요, 냉장고에 means in the refrigerator / in the fridge.

A useful pattern is:

[place]에 [thing]이/가 있어요
= There is/are [thing] in/at [place]

Here:

• 냉장고 = refrigerator, fridge
• 에 = location marker

So 냉장고에 tells you where the apple is.

In this sentence, 가 marks the thing that exists.

With 있다 meaning to exist / to be there, Korean often uses this pattern:

[place]에 [thing]이/가 있어요

So 사과가 있어요 literally means an apple exists / there is an apple.

Why not the others?

• 사과가: neutral, natural for introducing what is there
• 사과는: would add contrast or topic nuance, like as for the apple...
• 사과를: is an object marker, usually used with action verbs, not with existential 있다 in this pattern

So 사과가 is the most natural choice here.

있어요 is the polite present form of 있다.

In this sentence, 있어요 means there is / there are / is in / exists.

It does not mean an action like to put or to keep here. It simply says that something is present in a place.

So:

• 사과가 있어요 = There is an apple
• 냉장고에 사과가 있어요 = There is an apple in the fridge

Also, 있다 can mean to have in some contexts:

• 사과가 있어요 can also feel like I have apples, if the context makes that clear

But in this sentence, because a location is given, the meaning is clearly there is an apple in the fridge.

Korean often leaves out subjects when they are obvious or unnecessary.

English usually wants a subject, even a dummy one like there in There is an apple in the fridge. Korean does not need that.

So 냉장고에 사과가 있어요 is already a complete sentence.

There is no missing word that must be added. Korean simply allows you to state:

• the place
• the thing
• the existence

That is enough.

The most common order is:

[place]에 [thing]이/가 있어요

So: 냉장고에 사과가 있어요

This is the most natural basic order.

Korean word order is somewhat flexible because particles show the role of each word. So you might also hear:

사과가 냉장고에 있어요

This still means The apple is in the fridge.

The difference is mostly about emphasis:

• 냉장고에 사과가 있어요 focuses naturally on what is in the fridge
• 사과가 냉장고에 있어요 focuses more on where the apple is

By itself, 사과 does not show singular or plural the way English does.

So 사과가 있어요 could mean:

• There is an apple
• There are apples

Context usually tells you which one is meant.

If the speaker wants to make plural clearer, they might say:

• 사과들이 있어요 — but this is not always necessary and can sound marked depending on context
• or use a number, like 사과 두 개가 있어요 = There are two apples

In your sentence, English often translates it as There is an apple in the fridge, but Korean itself does not force that singular meaning.

있어요 is commonly pronounced more like 이써요.

That is because the final consonant in 있- affects the following sound.

So:

• spelling: 있어요
• common pronunciation: 이써요

This is very normal in Korean: pronunciation often changes slightly across syllable boundaries even though the spelling stays the same.

The dictionary form is 있다.

Here is the breakdown:

• 있다 = dictionary form
• 있어요 = polite present form

So if you look it up in a dictionary, search for 있다, not 있어요.

English often uses there is/there are for existence:

• There is an apple in the fridge

Korean does not use a word equivalent to English dummy there here.

Instead, Korean expresses existence with:

• a location marked by 에
• a noun marked by 이/가
• the verb 있다

So Korean is closer to: In the fridge, an apple exists

That sounds unnatural in English, so we translate it as: There is an apple in the fridge

있어요 is the polite, everyday style, often called the -어요/-아요 style.

It is appropriate in many normal situations:

• talking to strangers
• speaking politely to coworkers
• everyday conversation
• classroom situations

Related forms:

• 있다 = dictionary form, plain style
• 있어요 = polite everyday style
• 있습니다 = more formal polite style

So a more formal version of the sentence would be:

냉장고에 사과가 있습니다.

Normally, no.

Use 에 with 있다/없다 to mark where something exists.

• 냉장고에 사과가 있어요 = correct

에서 is usually used for the place where an action happens:

• 학교에서 공부해요 = I study at school
• 부엌에서 요리해요 = I cook in the kitchen

Since 있어요 here is not an action like studying or cooking, 에 is the correct particle.