الجورب تحت الكرسي.

In Arabic, the present tense of to be is usually not written or spoken in simple sentences like this.

So:

• الجورب تحت الكرسي
• literally: the sock under the chair
• natural English: The sock is under the chair

This is called a nominal sentence in Arabic. Arabic often just puts the subject first and then the description/location after it, without adding a separate word for is.

If you wanted was, then Arabic would use a verb, such as كان.

الـ is the Arabic definite article, meaning the.

So:

• الجورب = the sock
• الكرسي = the chair

Without الـ, the words would usually be indefinite:

• جورب = a sock
• كرسي = a chair

So the sentence with both definite nouns refers to a specific sock and a specific chair.

A careful pronunciation is:

al-jawrabu taḥta al-kursiyyi

In normal pause, many final short vowels are not pronounced, so a learner may hear something closer to:

al-jawrab taḥt al-kursī

A rough guide:

• الجورب = al-jawrab
• تحت = taḥt or taḥta
• الكرسي = al-kursī

Notes:

• ḥ in taḥt is a stronger, breathier sound than English h
• j in MSA is usually like the j in judge
• ū / ī are long vowels

تحت means under / beneath by itself, so Arabic does not need another preposition here.

So:

• تحت الكرسي = under the chair

This is normal Arabic structure.
You do not need something like في before تحت in this sentence.

Because the sentence is presenting the sock as the topic, and then telling you where it is.

So the structure is:

• الجورب = the subject/topic
• تحت الكرسي = the location/predicate

This is the most straightforward way to say The sock is under the chair.

Arabic can sometimes change word order for style, emphasis, or context, but this order is very common and natural.

It tells the location of the sock.

More specifically:

• تحت = under
• الكرسي = the chair

Together, تحت الكرسي means under the chair.

In grammar terms, this whole part functions like the predicate of the sentence: it tells us something about الجورب.

Because تحت needs something after it to show under what.

So:

• تحت = under
• تحت الكرسي = under the chair

This is similar to English, where under is followed by a noun phrase.

In more formal grammar terms, تحت is followed by a noun in a genitive relationship, so الكرسي comes after it.

With full case endings, the sentence is:

الجوربُ تحتَ الكرسيِّ

Breakdown:

• الجوربُ = nominative, because it is the subject/topic of the sentence
• تحتَ = usually treated as an adverb of place and appears in the accusative form
• الكرسيِّ = genitive, because it comes after تحت in this construction

However, in everyday reading and speaking, these endings are often not pronounced in pause, especially outside very formal contexts.

الجورب is masculine.

That matters when you later use pronouns or adjectives with it.

For example:

• الجورب جديد = The sock is new
• هو تحت الكرسي = It is under the chair
  (using the masculine pronoun هو)

Arabic nouns have grammatical gender, and learners need to memorize it along with the noun.

You would remove the definite article الـ from both nouns:

جوربٌ تحتَ كرسيٍّ

That means:

• جوربٌ = a sock
• كرسيٍّ = a chair

So:

• الجورب تحت الكرسي = The sock is under the chair
• جورب تحت كرسي = A sock is under a chair

In unvoweled writing, the difference is mainly the presence or absence of الـ.

Yes. كرسي is spelled with ي at the end.

The word is:

كرسي

This final ي is part of the word itself, not just a case ending.
The usual pronunciation is kursī, with a long ee sound at the end.

When case endings are fully shown, you may see:

• الكرسيُ
• الكرسيَ
• الكرسيِ

But in ordinary unvoweled writing, it is simply الكرسي.

Yes, absolutely.

Arabic often forms complete sentences very economically.
This sentence has everything needed:

• الجورب = what we are talking about
• تحت الكرسي = where it is

So even though it is short, it is a full and natural sentence in Arabic.

Yes. This is a very normal and correct way to express the idea in Modern Standard Arabic.

A native speaker would understand it immediately as:

The sock is under the chair.

In casual spoken Arabic, pronunciation and vocabulary might vary by dialect, but the MSA sentence itself is standard and natural.