هذه الغرفة مناسبة.

Because غرفة is a feminine singular noun, and the demonstrative this must agree with it.

• هذا = this for masculine singular nouns
• هذه = this for feminine singular nouns

So:

• هذا الكتاب = this book
• هذه الغرفة = this room

In Arabic, many nouns ending in ـة (called tāʾ marbūṭa) are feminine, and غرفة is one of them.

That feminine gender affects other words in the sentence, so you get:

• هذه instead of هذا
• مناسبة instead of a masculine form like مناسب

In Arabic, after a demonstrative like هذا / هذه, the noun is normally definite, so it usually takes الـ.

So Arabic says:

• هذه الغرفة

Literally, this is something like this the-room, but the natural English meaning is simply this room.

This is normal Arabic structure, not a special exception.

Because in Arabic, the verb to be is usually not stated in the present tense in simple sentences like this.

So:

• هذه الغرفة مناسبة literally looks like:
• this room suitable

But the natural meaning is:

• This room is suitable.

If you wanted past tense, Arabic would usually use كان:

• كانت هذه الغرفة مناسبة = This room was suitable

Because it is describing الغرفة, and adjectives in Arabic normally agree with the noun they describe in:

• gender
• number
• definiteness

Since الغرفة is feminine singular, the adjective is also feminine singular:

• masculine: مناسب
• feminine: مناسبة

So:

• غرفة مناسبة = a suitable room
• هذه الغرفة مناسبة = this room is suitable

Here, مناسبة is an adjective used as the predicate of the sentence.

The sentence is a nominal sentence:

• هذه الغرفة = the subject part
• مناسبة = the predicate, telling you something about the room

So it works like suitable / appropriate in English.

A learner may also notice that the same written form مناسبة can be a noun in other contexts, but here it is understood as the adjective suitable/appropriate.

The ending ـة (tāʾ marbūṭa) is usually pronounced like -a / -ah when you stop at the word.

So in normal paused pronunciation:

• غرفة → ghurfah
• مناسبة → munāsibah

But in fully inflected Arabic, when case endings are pronounced, it behaves like a t sound before the ending:

• الغرفةُ = al-ghurfatu
• مناسبةٌ = munāsibatun

So both ideas are useful:

• paused form: -ah
• fully inflected form: -at(u/n/i)

In fully vowelled MSA, the sentence is:

هذهِ الغرفةُ مناسبةٌ

Here is why:

• هذهِ: the demonstrative; it is basically fixed in form
• الغرفةُ: nominative, because it is the subject/topic of the nominal sentence
• مناسبةٌ: nominative, because it is the predicate

In everyday speech and in much reading practice, learners often hear or say the sentence without the final short vowels:

• هذه الغرفة مناسبة

It is a nominal sentence (جملة اسمية), meaning a sentence that begins with a noun-like element rather than a verb.

Structure here:

• هذه الغرفة = the topic / subject part
• مناسبة = the predicate

This is a very common Arabic pattern for simple descriptions:

• البيت كبير = the house is big
• المدينة جميلة = the city is beautiful
• هذه الغرفة مناسبة = this room is suitable

Yes, the l in الـ is pronounced here.

That is because غ is a moon letter, not a sun letter. So you say:

• al-ghurfah

not a doubled gh sound.

Compare:

• الغرفة → al-ghurfah because غ is a moon letter
• الشمس → ash-shams because ش is a sun letter and the l assimilates

Yes, but only if the thing being referred to is already clear from context.

• هذه مناسبة = this is suitable / this one is suitable
• هذه الغرفة مناسبة = this room is suitable

Including الغرفة makes the sentence more explicit and is often better for learners because the agreement is easier to see clearly.

The normal order is:

• هذه
  • the noun
    • the predicate

So:

• هذه الغرفة مناسبة

This is the standard MSA pattern for this/that + noun.

English speakers sometimes expect something more like الغرفة هذه, but that is not the normal MSA order for a basic sentence like this. In standard Arabic, putting the demonstrative first is the usual pattern here.