המסדרון צר מאוד, ולכן קשה לשים שם ארון.

In the present tense, Hebrew usually leaves out the verb to be.

So:

• המסדרון צר מאוד = The hallway is very narrow
• literally: The hallway very narrow

This is normal Hebrew. If you wanted past or future, then Hebrew would use forms of להיות (to be):

• המסדרון היה צר מאוד = The hallway was very narrow
• המסדרון יהיה צר מאוד = The hallway will be very narrow

Because צר here is a predicate adjective, not an adjective directly attached to the noun.

Compare:

• המסדרון הצר = the narrow hallway
  Here הצר describes the noun inside the noun phrase, so it takes ה.

• המסדרון צר = the hallway is narrow
  Here צר is the predicate, so it does not take ה.

This is a very important Hebrew pattern:

• הילד הקטן = the small boy
• הילד קטן = the boy is small

Because מסדרון is a masculine singular noun, and the adjective agrees with it.

• מסדרון = masculine singular
• therefore צר = masculine singular adjective form

If the noun were feminine, the adjective would change:

• הדרך צרה מאוד = The road is very narrow

So the agreement here is completely regular.

In Hebrew, מאוד (very) usually comes after the adjective or adverb it modifies.

So:

• צר מאוד = very narrow
• literally: narrow very

This is the normal order in Hebrew.

More examples:

• גדול מאוד = very big
• יפה מאוד = very beautiful
• לאט מאוד = very slowly

Putting מאוד before the adjective is generally not the standard neutral order.

ולכן means and therefore, and so, or simply so.

It is made of:

• ו־ = and
• לכן = therefore / therefore so

So:

• המסדרון צר מאוד, ולכן קשה... = The hallway is very narrow, and therefore / so it is hard...

It is a little more formal or written-sounding than just אז in some contexts, but it is still very common and natural.

This is a very common Hebrew structure:

• קשה + infinitive
• meaning: it is difficult to...

So:

• קשה לשים = it is hard to put

This is an impersonal expression. Hebrew does not need an explicit word like English it.

Similar examples:

• קשה להבין = It is hard to understand
• קל לראות = It is easy to see
• אסור לעשן = It is forbidden to smoke

So קשה לשים שם ארון is a standard way to say it is hard to put a cabinet there.

No. In this sentence, קשה is not describing ארון.

It is part of the impersonal structure:

• קשה לשים... = it is difficult to put...

So קשה is not saying that the cabinet is difficult. It is saying that the action of putting the cabinet there is difficult.

That is why you should understand the sentence as:

• Because the hallway is very narrow, it is difficult to put a cabinet there

not:

• Because the hallway is very narrow, a cabinet there is difficult

Because את is used before a definite direct object, and ארון here is indefinite.

Compare:

• לשים ארון = to put a cabinet / a closet
• לשים את הארון = to put the cabinet / the closet

Since the sentence means a cabinet, not the cabinet, there is no את.

This is one of the most important uses of את in Hebrew:

• definite object → use את
• indefinite object → do not use את

לשים means to put or to place.

It is the infinitive of the verb שם in the sense of put/place.

In everyday Hebrew, לשים is a very common general verb, much like English put. It works in many situations:

• לשים ספר על השולחן = to put a book on the table
• לשים את המפתחות בתיק = to put the keys in the bag

So in this sentence, לשים שם ארון simply means to put a cabinet there.

Here שם means there.

So:

• לשים שם ארון = to put a cabinet there

This word can be confusing because שם can also mean name, but the meaning is clear from context.

Compare:

• השם שלי דניאל = My name is Daniel
• הספר שם = The book is there

In your sentence, שם clearly means there, referring to the hallway.

Yes, it could.

For example:

• המסדרון צר מאוד, ולכן קשה לשים ארון במסדרון

This is grammatically fine, but it sounds more repetitive because מסדרון was just mentioned.

Using שם is more natural because it avoids repeating the noun:

• המסדרון צר מאוד, ולכן קשה לשים שם ארון

So שם works like English there, referring back to the previously mentioned place.

Because ארון is a fairly broad word for a storage piece of furniture.

Depending on context, it can mean things like:

• cabinet
• cupboard
• closet
• wardrobe

The exact English choice depends on what kind of ארון is meant.

In this sentence, since it is something being placed in a hallway, cabinet or closet may be the most natural translation, but the Hebrew itself does not always force one single English word.