الطوق وحاملة القطط كبيران.

Because the sentence has two things as its subject:

• الطوق = the collar
• حاملة القطط = the cat carrier

When Arabic talks about exactly two items together, it often uses the dual. So instead of كبير (big, singular), it becomes كبيران (big, dual, nominative).

So the structure is basically:

• الطوق وحاملة القطط = the collar and the cat carrier
• كبيران = are big

Because the two nouns are of mixed grammatical gender:

• الطوق is masculine
• حاملة is feminine

When Arabic has a mixed-gender pair, the default agreement is usually masculine. So the predicate becomes the masculine dual:

• masculine dual nominative: كبيران
• feminine dual nominative: كبيرتان

Since the pair is mixed, كبيران is the expected form.

Because كبيران is not functioning like a separate adjective attached to just one noun. It is the predicate of the whole sentence.

This is a nominal sentence:

• الطوق وحاملة القطط = the subject
• كبيران = the predicate

So Arabic is saying that both together have the property of being big.

This is similar to English The collar and the cat carrier are big, where big applies to both nouns together.

Because in this sentence كبيران is a predicate, not an attributive adjective directly modifying a noun.

In Arabic nominal sentences, the predicate is often indefinite, even if the subject is definite.

So:

• الطوق وحاملة القطط = definite subject
• كبيران = indefinite predicate

That is why you get كبيران, not الكبيران.

Because حاملة القطط is an iḍāfa construction, often called a possessive/genitive construction.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun determines whether the whole phrase is definite or indefinite

Here:

• حاملة = carrier
• القطط = the cats

Since the second part is definite (القطط), the whole phrase becomes definite:

• حاملة القطط = the cat carrier / the carrier of the cats

So even without الـ on حاملة, the whole phrase is definite.

Because in an iḍāfa construction, the first noun normally does not take الـ.

So Arabic says:

• حاملة القطط = the cat carrier

not:

• الحاملة القطط ❌

That would break the normal iḍāfa pattern.

A useful rule:

• in iḍāfa, definiteness usually appears on the second noun, not the first

حاملة is the feminine form of an active-participle-type word from the root meaning to carry.

Here it functions as a noun meaning something like:

• carrier
• holder
• case

So حاملة القطط means cat carrier.

It is feminine in form, which is why the noun itself is grammatically feminine.

Because القطط means the cats.

In the expression حاملة القطط, Arabic literally says something like carrier of the cats, which is a natural way to express cat carrier.

English often uses one noun in front of another noun, as in cat carrier, but Arabic commonly uses an iḍāfa structure instead.

Depending on context, Arabic might also use other phrasing, but حاملة القطط is a straightforward way to express the idea.

Because the phrase is referring to the cat carrier, not just a cat carrier.

Compare:

• حاملةُ القططِ = the cat carrier
• حاملةُ قططٍ = a cat carrier / a carrier for cats

When the second noun in iḍāfa is definite, the whole phrase becomes definite.

So القطط helps make حاملة القطط mean the cat carrier.

Because Arabic predicates usually come after the subject in a normal nominal sentence.

So the sentence order is:

• subject: الطوق وحاملة القطط
• predicate: كبيران

That gives:

• الطوق وحاملة القطط كبيران

This is very normal Arabic word order for X and Y are big.

It is in the nominative dual form.

The dual endings are commonly:

• ـانِ / -ān(i) for nominative
• ـيْنِ / -ayn(i) for accusative/genitive

Here كبيران is nominative because it is the predicate of a nominal sentence in standard grammar.

So:

• كبيران = nominative dual
• not كبيرين, which would be accusative/genitive dual

Because Arabic distinguishes clearly between:

• two things → dual
• three or more things → plural

Since the subject contains exactly two coordinated nouns, using the dual is appropriate:

• كبيران = two things are big

If there were three or more items, Arabic would normally use a plural form instead.

Yes, الطوق is grammatically masculine.

That matters here because the full subject is made up of:

• one masculine noun: الطوق
• one feminine noun: حاملة القطط

Since the pair is mixed, Arabic uses masculine agreement for the dual predicate, giving كبيران.

Yes. Grammatically, that is exactly how the sentence works:

• الطوق = the collar
• و = and
• حاملة القطط = the cat carrier
• كبيران = are big

So the sentence is a straightforward nominal sentence with a coordinated subject and a dual predicate.