سلسلة الدراجة نظيفة.

Because Arabic often leaves out the verb to be in the present tense.

So:

سلسلة الدراجة نظيفة
literally: the bicycle chain clean
naturally: The bicycle chain is clean.

This is called a nominal sentence in Arabic. In the present tense, Arabic usually does not use a separate word for is / am / are.

If you wanted the past tense, then Arabic would use a verb, for example:

كانت سلسلة الدراجة نظيفة = The bicycle chain was clean.

This is an iḍāfa construction, often called a genitive construction.

It is made of:

• سلسلة = chain
• الدراجة = the bicycle

Together, literally, it means:

• chain of the bicycle

In English, we usually translate that more naturally as:

• the bicycle chain

So Arabic is expressing possession or close relationship by putting the two nouns next to each other.

That is a normal feature of the iḍāfa construction.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can be definite with الـ
• if the second noun is definite, the whole phrase becomes definite

So:

• سلسلة الدراجة = the bicycle’s chain / the bicycle chain

Even though سلسلة does not have الـ, the whole phrase is definite because الدراجة is definite.

Because that would not be the normal iḍāfa pattern.

In an iḍāfa, the first noun does not take الـ. So you say:

• سلسلة الدراجة = the bicycle chain

not:

• السلسلة الدراجة

Also, السلسلة الدراجة would sound like two separate definite words and would not correctly express the relationship chain of the bicycle.

Because it describes سلسلة, and سلسلة is a feminine singular noun.

In Arabic, adjectives agree with the noun they describe in gender and number.

So:

• سلسلة = feminine singular
• therefore نظيفة = feminine singular

If the noun were masculine, you would use نظيف instead.

For example:

• القلم نظيف = The pen is clean
• السلسلة نظيفة = The chain is clean

One strong clue is the ending ة (called tāʾ marbūṭa).

Many Arabic nouns ending in ة are feminine, including:

• سلسلة = chain
• دراجة = bicycle
• سيارة = car

So سلسلة is grammatically feminine, and that is why the adjective must also be feminine: نظيفة.

Because here نظيفة is the predicate of the sentence, not an adjective inside the noun phrase.

Arabic distinguishes between:

1. attributive adjective: directly attached to a noun
2. predicate adjective: part of the sentence meaning is clean

Here we have a full sentence:

• سلسلة الدراجة نظيفة = The bicycle chain is clean

Since نظيفة is the predicate, it is normally indefinite, so it does not take الـ.

Compare:

• سلسلة الدراجة النظيفة = the clean bicycle chain
  Here النظيفة is an attributive adjective inside the noun phrase, so it is definite.

• سلسلة الدراجة نظيفة = The bicycle chain is clean
  Here نظيفة is the predicate, so it stays indefinite.

Because سلسلة الدراجة acts as one complete noun phrase: the bicycle chain.

Only after that full phrase do we get the predicate:

• سلسلة الدراجة = subject
• نظيفة = predicate

So the structure is:

• [the bicycle chain] [clean]

If you put the adjective inside the noun phrase, the meaning changes:

• سلسلة الدراجة النظيفة = the chain of the clean bicycle or more naturally the clean bicycle’s chain, depending on context

So position matters a lot.

With full case endings, it would be:

سِلْسِلَةُ الدَّرَّاجَةِ نَظِيفَةٌ

A careful pronunciation guide:

• sil-si-la-tu = سِلْسِلَةُ
• ad-dar-rā-ja-ti = الدَّرَّاجَةِ
• na-ẓī-fa-tun = نَظِيفَةٌ

In normal everyday reading, short vowels are usually not written, so you will often just see:

سلسلة الدراجة نظيفة

In fully vocalized MSA:

سِلْسِلَةُ الدَّرَّاجَةِ نَظِيفَةٌ

The endings are:

• سلسلةُ: ḍamma because it is the subject of the nominal sentence
• الدراجةِ: kasra because the second noun in an iḍāfa is in the genitive case
• نظيفةٌ: ḍamma + tanwīn because it is an indefinite predicate

So grammatically:

• subject: سلسلةُ الدراجةِ
• predicate: نظيفةٌ

In pause, especially in normal speech, these final endings are often not pronounced clearly.

Because سلسلة is the first term of an iḍāfa construction.

The first noun in an iḍāfa:

• does not take الـ
• does not take tanwīn

So you get:

• سلسلةُ الدراجةِ

not:

• سلسلةٌ الدراجةِ

That is one of the standard signs that a noun is the first part of an iḍāfa.

No, not naturally in this exact form.

Because سلسلة الدراجة is a definite iḍāfa, it means the bicycle chain or the chain of the bicycle, not a bicycle chain.

If you wanted something more indefinite like a bicycle chain is clean, the Arabic structure would be different and would depend on the intended meaning.

So in this sentence, the subject is understood as definite.

They mean different things:

• السلسلة نظيفة = The chain is clean
• سلسلة الدراجة نظيفة = The bicycle chain is clean

The second sentence is more specific because it tells you which chain: the one belonging to the bicycle.

So الدراجة is narrowing down the meaning of سلسلة.

Yes. That is the literal translation.

But in natural English, we usually prefer:

• the bicycle chain

Both are correct in meaning. English often turns Arabic iḍāfa constructions into compact noun phrases.

So:

• literal: the chain of the bicycle
• natural: the bicycle chain

The pattern is:

[definite noun phrase] + [indefinite predicate adjective]

So here:

• سلسلة الدراجة = definite noun phrase
• نظيفة = predicate adjective

This is a very common Arabic pattern, for example:

• البيت كبير = The house is big
• السماء صافية = The sky is clear
• سلسلة الدراجة نظيفة = The bicycle chain is clean

It is one of the most useful basic patterns in MSA.