لم يكنس المتطوعون نقطة التجمع.

لم is a negation particle used for the past in Standard Arabic.

It is followed by the imperfect verb, but that verb becomes jussive in form. So:

• يكنسُ = he sweeps / is sweeping
• لم يكنسْ = he did not sweep

So لم يكنس المتطوعون... means the volunteers did not sweep...

This is a very common Arabic pattern:

• لم + imperfect verb (jussive) = did not + verb

Because the sentence uses the common verb-subject-object order:

• لم يكنس = did not sweep
• المتطوعون = the volunteers

In Standard Arabic, when the verb comes before an explicit plural subject, the verb is often kept in the singular form.

So this is normal:

• لم يكنس المتطوعون نقطة التجمع

If you put the subject first, then the verb usually shows full plural agreement:

• المتطوعون لم يكنسوا نقطة التجمع

Both are correct, but the agreement pattern changes with word order.

Yes. Very normal.

The basic formal Arabic word order is often:

• Verb - Subject - Object

So here you have:

• لم يكنس = did not sweep
• المتطوعون = the volunteers
• نقطة التجمع = the assembly point

English usually prefers Subject - Verb - Object, so this can feel unusual at first, but in Arabic it is standard.

Because المتطوعون is a sound masculine plural in the nominative case.

Its singular is:

• متطوع = volunteer

Its plural is:

• متطوعون in the nominative
• متطوعين in the accusative/genitive

Here it is the subject of the verb, so it is nominative:

• المتطوعون = the volunteers

That -ون ending is one of the most recognizable plural endings in Arabic.

Because نقطة التجمع is an iḍāfa construction, often called a construct phrase.

Literally, it is something like:

• point of the assembly/gathering

In an iḍāfa:

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

So:

• نقطة تجمع = an assembly point / a gathering point
• نقطة التجمع = the assembly point

Since التجمع is definite, the whole phrase becomes definite.

Because it is the second part of an iḍāfa.

In Arabic, the second noun in an iḍāfa is always genitive.

So:

• نقطةَ = point, in the accusative here because it is the direct object
• التجمعِ = of the assembly/gathering, in the genitive because it is the second term of the iḍāfa

So grammatically:

• نقطةَ التجمعِ = the assembly point

In full grammatical form:

• المتطوعون is nominative because it is the subject
• نقطةَ is accusative because it is the direct object
• التجمعِ is genitive because it is the second noun in an iḍāfa

So the fully parsed structure is:

• لم يكنس = verb phrase
• المتطوعون = subject, nominative
• نقطةَ التجمعِ = object phrase, with نقطةَ accusative and التجمعِ genitive

A fully vowelled version would be:

لَمْ يَكْنُسِ الْمُتَطَوِّعُونَ نُقْطَةَ التَّجَمُّعِ

A few notes:

• After لم, the verb is underlyingly يكنسْ in the jussive
• In connected reading, a helping vowel may appear before الـ to avoid two consonants meeting awkwardly, which is why you may see يكنسِ
• نقطةَ shows the accusative ending
• التجمعِ shows the genitive ending

In normal everyday Arabic writing, these short vowels are usually omitted.

Yes. That is also correct.

Compare:

• لم يكنس المتطوعون نقطة التجمع
  Verb first, so the verb stays singular

• المتطوعون لم يكنسوا نقطة التجمع
  Subject first, so the verb agrees fully in the plural

The second version can feel a bit more like The volunteers did not sweep the assembly point, with slightly more attention on the volunteers.

Because لم is the standard way to say did not in formal Arabic.

Compare:

• لم يكنس = did not sweep
• لا يكنس = does not sweep / is not sweeping in a general-present sense
• ما كنس = did not sweep

So لم is the best choice for a clear, standard past negative in MSA.

A helpful comparison:

• لم يكنس = did not sweep
• لا يكنس = does not sweep
• لن يكنس = will not sweep

Because ت is a sun letter.

When الـ comes before a sun letter, the ل sound is not pronounced, and the next consonant is doubled in pronunciation.

So:

• written: التجمع
• pronounced: at-tajammuʿ

This happens in many common words, for example:

• الشمس is pronounced ash-shams
• الطالب is pronounced aṭ-ṭālib? No, actually طالب starts with ط, so aṭ-ṭālib
• التجمع is pronounced at-tajammuʿ

The spelling stays the same, but the pronunciation changes.