السطح نظيف.

In Arabic, the verb to be is usually not stated in the present tense.

So:

• السطح نظيف = The surface is clean

This is called a nominal sentence. Arabic often simply puts:

• the subject
  • the description

If you want past or future, Arabic does use a verb:

• كان السطح نظيفًا = The surface was clean
• سيكون السطح نظيفًا = The surface will be clean

So in the present tense, leaving out is is completely normal.

Because السطح is the subject and it is definite: the surface.

But نظيف is the predicate adjective: clean.

In Arabic, when you say X is Y, the pattern is often:

• definite noun
  • indefinite adjective/noun

So:

• السطح نظيف = The surface is clean

If you added الـ to نظيف, you would get:

• السطح النظيف

That does not mean The surface is clean.
It means the clean surface.

So the presence or absence of الـ changes the structure a lot.

This is a very important difference:

• السطح نظيف = The surface is clean
• السطح النظيف = the clean surface

In the first one, نظيف is a predicate saying something about the surface.

In the second one, النظيف is an adjective directly modifying السطح.

A helpful way to see it:

• noun + indefinite adjective often gives a full sentence
• noun + definite adjective often gives a noun phrase

So:

• البيت كبير = The house is big
• البيت الكبير = the big house

In careful spelling, it begins with الـ, but in pronunciation the ل of الـ is assimilated because س is a sun letter.

So السطح is pronounced approximately:

• as-saṭḥ

not:

• al-saṭḥ

The spelling stays the same, but the pronunciation changes.

With full vowels, it is:

• السَّطْحُ
• approximately as-saṭḥu

This is a common feature of Arabic definite article pronunciation.

It is an adjective, but in this sentence it functions as the predicate of the sentence.

So grammatically:

• السطح = the subject
• نظيف = the predicate adjective

English also does this:

• The surface = subject
• clean = predicate adjective in The surface is clean

So نظيف is still an adjective, but it is not directly attached to the noun the way it would be in السطح النظيف.

Yes. In Arabic, adjectives agree with the noun they describe in things like:

• gender
• number
• often case as well in fully vocalized Arabic

Here:

• السطح is masculine singular
• so نظيف is also masculine singular

If the noun were feminine, the adjective would usually be feminine too. For example:

• الغرفة نظيفة = The room is clean

So agreement is important.

In fully vocalized Modern Standard Arabic, it is:

• السَّطْحُ نَظِيفٌ

Why?

• السَّطْحُ ends in ـُ because it is the subject of a nominal sentence, so it is nominative
• نَظِيفٌ also ends in ـٌ because it is the predicate and is also nominative

So the full form is:

• السَّطْحُ نَظِيفٌ

In normal writing and everyday pronunciation, these short endings are often not written or not clearly pronounced, especially at pause.

Because it is indefinite.

In the sentence:

• السَّطْحُ نَظِيفٌ

the word نظيفٌ is not the clean, but simply clean. Since it is indefinite, it takes tanwīn in full vocalization.

Compare:

• نظيفٌ = clean / a clean one
• النظيفُ = the clean

This helps show the difference between:

• السطح نظيف = The surface is clean
• السطح النظيف = the clean surface

Yes, but for a beginner, السطح نظيف is the normal and safest pattern.

This sentence follows the common order:

• subject
  • predicate

Arabic can sometimes move things around for emphasis, especially in formal or literary styles, but the basic beginner pattern is:

• البيت كبير
• الجو جميل
• السطح نظيف

So it is best to learn this order first.

A very common way is:

• السطح ليس نظيفًا = The surface is not clean

Here ليس is used to negate nominal sentences in the present.

Another possible way is:

• السطح غير نظيف = The surface is not clean / The surface is unclean

A note on the first form:

• نظيفًا appears with fatḥa/tanwīn fatḥ after ليس

So if you are learning standard grammar, both the positive and negative patterns are useful:

• السطح نظيف
• السطح ليس نظيفًا

Yes. It is a very natural and standard kind of Arabic sentence.

It uses a very common structure:

• definite noun
  • indefinite adjective

This pattern is one of the most basic and useful sentence types in Arabic, for example:

• الكتاب مفيد = The book is useful
• الطقس جميل = The weather is beautiful
• السطح نظيف = The surface is clean

So this is an excellent model sentence for learning Arabic grammar.