هذه مسؤولية كبيرة.

Because هذه is the feminine form of this, and مسؤولية is a feminine noun.

In Arabic, demonstratives must agree with the noun they refer to:

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

So:

• هذا كتاب = this is a book
• هذه مسؤولية = this is a responsibility

Even though مسؤولية does not end with the usual ـة, it is still grammatically feminine.

مسؤولية is a feminine noun by grammar and usage. Many abstract nouns in Arabic are feminine, and nouns ending in ـية are very often feminine.

So even though it may not look like the most familiar feminine ending to a beginner, it still behaves as feminine in agreement:

• هذه مسؤولية
• مسؤولية كبيرة

That is why both the demonstrative هذه and the adjective كبيرة are feminine.

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

So هذه مسؤولية كبيرة literally looks like:

• this
• a responsibility
• big

But it means:

• This is a big responsibility

This kind of sentence is very normal in Arabic. It is called a nominal sentence.

If you wanted the past or future, Arabic would use an actual verb:

• كانت هذه مسؤولية كبيرة = This was a big responsibility
• ستكون هذه مسؤولية كبيرة = This will be a big responsibility

Because adjectives normally come after the noun in Arabic.

So:

• مسؤولية كبيرة = a big responsibility

This is the normal order:

• noun + adjective

Compare:

• كتاب كبير = a big book
• مدينة كبيرة = a big city
• مسؤولية كبيرة = a big responsibility

Because the adjective must agree with the noun it describes.

Since مسؤولية is:

• feminine
• singular
• indefinite

the adjective must also be:

• feminine
• singular
• indefinite

So:

• مسؤولية كبيرة = a big responsibility

If the noun were masculine, you would use كبير:

• أمر كبير = a big matter

In Arabic, adjectives match the noun in definiteness as well as gender and number.

Here, مسؤولية is indefinite, meaning a responsibility, not the responsibility. So the adjective must also be indefinite:

• مسؤولية كبيرة = a big responsibility

If the noun were definite, the adjective would also be definite:

• المسؤولية الكبيرة = the big responsibility

So the rule is:

• indefinite noun -> indefinite adjective
• definite noun -> definite adjective

Yes. It is a complete and natural sentence in Modern Standard Arabic.

It has:

• هذه as the subject-like element
• مسؤولية كبيرة as the predicate

So it fully expresses the idea This is a big responsibility without needing anything else.

In fully vocalized MSA, it would typically be:

هٰذِهِ مَسْؤُولِيَّةٌ كَبِيرَةٌ

The final ـٌ on مسؤولية and كبيرة shows that they are indefinite in the nominative case.

However, in normal everyday writing, these short vowels and case endings are usually omitted, so you usually see:

هذه مسؤولية كبيرة

Both are correct; the second is just the normal unvoweled spelling.

It is usually pronounced approximately as:

mas-ʔuu-liy-ya

A few things to notice:

• The ء is a hamza, a glottal stop.
• The و here helps make a long uu sound.
• The ending ـية is often heard like -iyya.

So the word has several parts:

• مس = mas
• ؤو = ʔuu
• لي = liy
• ة in this pattern contributes to the final -ya / -yah type ending in careful pronunciation

Learners often find this word a little tricky because of the hamza.

No, not in normal standard Arabic for this meaning.

To say a big responsibility, Arabic uses:

• مسؤولية كبيرة

The adjective follows the noun. So:

• هذه مسؤولية كبيرة = correct
• هذه كبيرة مسؤولية = not the normal structure

Not exactly in its current form.

هذه مسؤولية كبيرة most naturally means:

• This is a big responsibility

If you want to say This responsibility is big, you would usually say:

• هذه المسؤولية كبيرة

Why?

• هذه مسؤولية كبيرة = this is a big responsibility
• هذه المسؤولية كبيرة = this responsibility is big

The presence of ال on المسؤولية changes the structure and meaning.

It is a nominal sentence in Arabic.

A simple way to understand it:

• هذه = the topic or subject-like part
• مسؤولية كبيرة = the comment or predicate about it

Traditional Arabic grammar would often analyze it as:

• هذه = مبتدأ
• مسؤولية كبيرة = خبر

You do not need to master those labels immediately, but it helps to know that Arabic often builds sentences without a present-tense verb, especially in statements like this.

Yes. The pattern stays the same:

هذه + noun + adjective

For example:

• هذه مسؤولية صعبة = This is a difficult responsibility
• هذه مسؤولية مهمة = This is an important responsibility
• هذه مسؤولية مشتركة = This is a shared responsibility

Just remember that the adjective must agree with مسؤولية, so it should be feminine singular.