هذه القصة مضحكة.

A careful MSA pronunciation is:

hādhihi al-qiṣṣatu muḍḥikatun

In normal pausal pronunciation, you will often hear it more like:

hādhihi al-qiṣṣa muḍḥika

A few notes:

• هذه = hādhihi
• القصة = al-qiṣṣa
• مضحكة = muḍḥika

Also:

• ق is a deep q sound, not an English k
• ص is an emphatic s
• ض is an emphatic d
• the doubled صّ in القصة should be held a little longer

هذه means this for a feminine singular noun.

Since قصة (story) is a feminine singular noun, Arabic uses هذه rather than هذا.

So:

• هذا = this (masculine singular)
• هذه = this (feminine singular)

Because قصة is feminine, the sentence must begin with هذه.

In Arabic, nouns have grammatical gender. قصة is grammatically feminine.

One very common sign of a feminine noun is the ending ة (called tāʾ marbūṭa).
Since قصة ends in ة, it is feminine.

This is why both:

• the demonstrative هذه
• and the adjective مضحكة

are also feminine.

ال is the Arabic definite article, meaning the.

So:

• قصة = a story
• القصة = the story

In this sentence, the meaning is this story, so Arabic uses the definite noun القصة.

That is very normal in Arabic: after a demonstrative like هذا / هذه, the noun is usually definite.

Adjectives in Arabic must agree with the noun they describe.

Since القصة is:

• feminine
• singular
• definite

the adjective must match the feminine singular part. So:

• masculine: مضحك = funny
• feminine: مضحكة = funny

Here, مضحكة is feminine because it refers to القصة.

In Arabic, adjectives normally come after the noun they describe.

So Arabic says:

• القصة المضحكة = the funny story

not the equivalent of English funny story with the adjective first.

In your sentence, مضحكة comes after القصة, which is the normal Arabic order.

In the present tense, Arabic usually does not use a separate word for is / am / are in simple sentences like this.

So:

• هذه القصة مضحكة literally looks like this story funny
• but it means this story is funny

This is completely normal in Arabic.

If you wanted the past tense, then Arabic would use a verb such as كانت:

• هذه القصة كانت مضحكة = this story was funny

Because it is the predicate of the sentence, not an attributive adjective inside a noun phrase.

Compare these two:

1. هذه القصة مضحكة
   = This story is funny.

2. هذه القصة المضحكة
   = This funny story.

In sentence 1, مضحكة is the predicate, so it is normally indefinite and does not take ال.

In sentence 2, المضحكة directly describes القصة inside the noun phrase, so it matches it in definiteness and takes ال.

This is a very important Arabic distinction.

A fully vowelled version is:

هٰذِهِ الْقِصَّةُ مُضْحِكَةٌ

This shows the grammatical endings more clearly:

• هٰذِهِ
• الْقِصَّةُ
• مُضْحِكَةٌ

At the end of a sentence, these short final vowels are often not pronounced clearly in everyday reading aloud, but they are important for grammar.

The final ة is called tāʾ marbūṭa.

Usually:

• when pausing, it is pronounced like -a
• when followed by grammatical endings in careful speech, it behaves like -t

So:

• in pause: qiṣṣa
• in full formal pronunciation with case ending: qiṣṣatu

The same is true for مضحكة:

• in pause: muḍḥika
• in full form: muḍḥikatun

Here it functions as an adjective/predicate adjective, meaning funny or amusing.

More specifically, it comes from the pattern of an active participle:

• masculine: مُضْحِك
• feminine: مُضْحِكَة

It describes something that causes laughter or is amusing.

So in this sentence, مضحكة means the story is amusing/funny.

In standard Arabic, after هذه, the normal form is هذه القصة.

So:

• هذه القصة مضحكة = the standard and expected form

Using هذه قصة مضحكة is generally not the standard MSA pattern for this is a funny story.

If you want to say This is a funny story, standard Arabic would usually still use the definite noun after the demonstrative:

• هذه قصةٌ مضحكةٌ is less standard in this exact demonstrative-noun pattern in MSA
• هذه القصة مضحكة is the regular model for this story is funny

For learners, the safe rule is:

• after هذا / هذه, use the noun with ال

This is a nominal sentence in Arabic, meaning a sentence built without a present-tense verb.

Its basic structure is:

• هذه القصة = the topic/subject
• مضحكة = the comment/predicate

So the sentence is made of:

1. a definite noun phrase: هذه القصة
2. a predicate: مضحكة

That is one of the most basic and common sentence patterns in Arabic.

Yes, Arabic ال sometimes changes in pronunciation depending on the next letter.

Here, the next letter is ق, which is a moon letter, so the l sound is pronounced clearly:

• الْقِصَّة = al-qiṣṣa

If the next letter were a sun letter, the l sound would assimilate instead.

So in this word, pronounce it clearly as al-, not with assimilation.