Cent personnes arrivent.

In French, numbers usually go directly before the noun, with no article:

• trois livres
• vingt étudiants
• cent personnes

So cent personnes is normal.

You would add an article only if you mean a specific set of people already identified:

• les cent personnes = the 100 people

Without an article, Cent personnes arrivent simply means 100 people are arriving / arrive.

Because ordinary cardinal numbers in French are followed directly by the noun:

• cent personnes
• mille euros
• deux chats

You use de after expressions like:

• une centaine de personnes = about a hundred people
• beaucoup de personnes = many people

So:

• cent personnes ✔
• cent de personnes ✘

Here, cent means 100, and in this sentence it stays singular in spelling: cent personnes.

A useful rule is:

• cent takes an s only when it is multiplied and not followed by another number.

Examples:

• cent personnes = 100 people
• deux cents euros = 200 euros
• deux cent un euros = 201 euros

So in your sentence, cent is correct, not cents.

Because the sentence is talking about 100 people, so the noun must be plural.

• une personne = one person
• deux personnes = two people
• cent personnes = one hundred people

French works the same way as English here: a number greater than one normally makes the noun plural.

Yes and no.

Personne is a feminine noun, so if you add adjectives or determiners, they must agree with it:

• cent personnes françaises
• ces personnes

But in this sentence, the verb arrivent is plural because the subject is plural.
Its form here is not feminine-specific.

So:

• gender matters for noun-related agreement
• number matters for the verb here

Because the subject, cent personnes, is plural.

French verbs must agree with the subject:

• Une personne arrive. = One person arrives.
• Cent personnes arrivent. = One hundred people arrive.

So arrivent is the correct third-person plural form of arriver.

No. In this form, the -ent ending is silent.

So arrivent is pronounced like arrive:

• arrive → /a.ʁiv/
• arrivent → /a.ʁiv/

That means:

• il arrive
• ils arrivent

sound the same in normal speech.

In the full sentence, a normal pronunciation is roughly:

• cent → nasal vowel, final t silent
• personnes → final s silent
• arrivent → final -ent silent

Approximate pronunciation: sahn pair-sonn ah-reev

More precisely: /sɑ̃ pɛʁ.sɔn a.ʁiv/

Normally, no.

• cent ends in a silent t here because the next word, personnes, starts with a consonant.
• personnes usually does not make a liaison before arrivent in ordinary speech.

So you normally say the words separately:

cent / personnes / arrivent

If cent were followed by a vowel sound, you might hear a liaison:

• cent amis → the t can be pronounced

But not in cent personnes.

By default, cent personnes usually means exactly 100 people.

If you want to sound approximate, French often uses:

• une centaine de personnes = about a hundred people
• environ cent personnes = around 100 people

So:

• Cent personnes arrivent. = 100 people are arriving / arrive
• Une centaine de personnes arrivent. = About a hundred people are arriving

Yes. The French present tense often covers both ideas, depending on context.

So Cent personnes arrivent can mean:

• One hundred people arrive
• One hundred people are arriving

French does have ways to emphasize an action in progress, but the simple present is very often enough.

Sometimes, but personnes is the safer and more neutral choice here.

• personnes = people/persons
• gens = people

Gens is common in everyday French, but it has some special grammar behavior and is not always as straightforward for learners.
In a simple sentence like this, cent personnes arrivent is very natural and easy to build correctly.

So yes, gens exists, but personnes is the better beginner-friendly word in this sentence.