البنطال في الحقيبة.

In Arabic, the present tense of to be is usually not written or spoken in simple sentences like this.

So Arabic says:

• البنطال في الحقيبة

  instead of literally saying:

• The trousers are in the bag

The idea of is/are is understood automatically from the structure.

This is a nominal sentence in Arabic, often called jumla ismiyya.

It has two main parts:

• البنطال = the topic/subject
• في الحقيبة = the predicate, a prepositional phrase telling where it is

So the structure is basically:

• [noun] + [prepositional phrase]

الـ is the Arabic definite article, meaning the.

So:

• البنطال = the trousers / the pants
• الحقيبة = the bag

Both nouns are definite here, just as they would be in English if you say The trousers are in the bag.

If you wanted them indefinite, you could say something like:

• بنطالٌ في حقيبةٍ = a pair of trousers is in a bag

In Arabic, بنطال is grammatically singular, even though English often treats pants/trousers as plural.

So Arabic thinks of it as one item of clothing.

That means if you add an adjective, it will usually be singular too:

• البنطال جديد = the trousers are new

Not a plural adjective.

Also, بنطال is grammatically masculine.

في means in.

It is a preposition, and in Arabic prepositions make the following noun genitive.

So in fully vowelled Arabic, you would write:

• البنطالُ في الحقيبةِ

Notice:

• البنطالُ ends with ـُ because it is the subject/topic
• الحقيبةِ ends with ـِ because it comes after في

In normal unvowelled writing, those endings are usually not shown.

A careful full pronunciation with case endings is:

• al-binṭālu fī al-ḥaqībati

In normal pause, especially at the end of the sentence, speakers often do not pronounce the final short vowels, so it may sound more like:

• al-binṭāl fī al-ḥaqība

Also, in both words the ل of الـ is pronounced normally, because:

• ب is a moon letter
• ح is also a moon letter

So there is no assimilation here.

That final ة is called tāʾ marbūṭa.

Its pronunciation depends on context:

• At the end of a paused word, it is usually pronounced like -a or -ah
  • حقيبة → ḥaqība
• In careful connected reading with case endings, the t sound appears:
  • الحقيبةِ → al-ḥaqībati

So both of these ideas are useful:

• dictionary-style / pause pronunciation: ḥaqība
• full grammatical pronunciation: ḥaqībati

• بنطال is masculine
• حقيبة is feminine

In this sentence, gender does not visibly change much, because there is no adjective or past/present verb agreeing with them.

But if you add adjectives, they must match the noun:

• البنطال الأسود = the black trousers
• الحقيبة الكبيرة = the big bag

So gender matters a lot in Arabic, even if this short sentence does not show much agreement yet.

Yes, but البنطال في الحقيبة is the most straightforward neutral order for this meaning.

If you move the prepositional phrase first:

• في الحقيبة البنطال

that becomes more marked and usually sounds like you are emphasizing the location.

Very often, fronting the location sounds especially natural when the noun is indefinite, for example:

• في الحقيبة بنطالٌ = there is a pair of trousers in the bag

So word order can change, but it may change the emphasis.

An iḍāfa is a noun-to-noun possession structure such as:

• حقيبةُ الرجلِ = the man’s bag

But in البنطال في الحقيبة, the two nouns are not directly linked as possession.

Instead, they are connected by the preposition في:

• في الحقيبة = in the bag

So this is not noun + noun possession. It is noun + prepositional phrase.

حقيبة is a broad word. Depending on context, it can mean:

• bag
• case
• suitcase

So the exact English translation may vary with the situation. The grammar of the Arabic sentence stays the same either way.