Avant que les invités arrivent, nous passons la serpillière dans la cuisine pour que le carrelage soit propre.

It means to mop the floor.

Literally, it looks like to pass the mop, but in normal French this expression simply means to mop. French often uses the cleaning tool as the direct object:

• passer l’aspirateur = to vacuum
• passer la serpillière = to mop

So nous passons la serpillière dans la cuisine means we mop the kitchen floor.

French usually uses an article where English often does not. With many fixed expressions involving body parts, tools, and everyday objects, the definite article is normal.

So French says:

• passer la serpillière
• passer l’aspirateur
• laver les mains

Even though English would say mop, vacuum, or wash your hands without the same structure.

Because dans is the normal preposition for something happening inside a room or enclosed space.

So:

• dans la cuisine = in the kitchen
• dans la salle de bain = in the bathroom

Using à la cuisine would not sound natural here. À is used for many locations in French, but for being physically inside a room, dans is usually the right choice.

Use avant que when it is followed by a clause with its own subject.

Here you have:

• les invités arrivent = the guests arrive

That is a full clause with a subject (les invités) and a verb (arrivent), so French needs avant que.

Use avant de when the subject stays the same and you can use an infinitive.

For example:

• Avant de partir, nous passons la serpillière.
  = Before leaving, we mop.

So the difference is:

• avant que + subject + verb
• avant de + infinitive

Yes. After avant que, French normally uses the subjunctive.

So grammatically, this is:

• avant que les invités arrivent

The tricky part is that with many -er verbs, the present subjunctive form looks exactly like the present indicative form in writing:

• indicative: ils arrivent
• subjunctive: qu’ils arrivent

So you cannot see the difference just from the spelling here, but the structure avant que tells you it is subjunctive.

Because avant que refers to something that has not happened yet at the moment of the main action. French often uses the subjunctive after conjunctions that express uncertainty, anticipation, purpose, emotion, or non-realized events.

In this sentence, the guests have not arrived yet when the mopping happens, so French uses the subjunctive:

• avant que les invités arrivent

English does not mark this the same way, so this is something learners usually just have to get used to.

Because pour que also triggers the subjunctive.

Pour que means so that / in order that, and it introduces a purpose. After it, French normally uses the subjunctive:

• pour que le carrelage soit propre

Here soit is the subjunctive of être.

So:

• est = indicative
• soit = subjunctive

After pour que, soit is the correct choice.

Not in this sentence.

French uses pour + infinitive when the subject is the same as in the main clause.

For example:

• Nous nettoyons la cuisine pour impressionner les invités.

Here nous are the ones doing the action of impressionner, so the infinitive works.

But in your sentence, the subordinate clause is about le carrelage, not nous:

• pour que le carrelage soit propre

Since it has its own subject, French uses pour que + subjunctive.

Le carrelage means the tiling or the tiled floor/surface. In this sentence, it most naturally refers to the kitchen floor tiles.

It is more specific than le sol, which just means the floor in general.

So:

• le sol = the floor
• le carrelage = the tiled floor / the tiles / the tiling

The sentence chooses carrelage because kitchens often have tile flooring, and the speaker wants to be specific.

Because propre agrees with le carrelage, which is singular.

Even though English might think of tiles as plural, French uses the singular noun carrelage to talk about the tiled surface as a whole.

So:

• le carrelage = singular masculine
• propre = singular masculine adjective

If the noun were plural, the adjective would change:

• les carreaux sont propres = the tiles are clean

Les invités usually means the guests in the sense of the specific guests expected for a particular occasion.

French often uses the definite article when the people or things are already understood from the context.

So here:

• les invités = the guests we are expecting

If you said des invités, it would sound more like some guests rather than a known group.

It is the present tense, but the French present can often be used for:

• a habitual action
• a planned action
• something understood from context as happening before a future event

So this sentence could mean something like:

• Before the guests arrive, we mop the kitchen floor...
• or we’re mopping the kitchen floor...

French does not need a future tense here. English also often uses the present after before:

• Before the guests arrive, we mop the floor.

So this part is actually quite similar in the two languages.

Sometimes, yes. In more formal or literary French, you may see an extra ne after avant que:

• avant que les invités n’arrivent

This ne is called an expletive ne. It does not make the sentence negative. It is just a stylistic or grammatical feature found with certain expressions.

In everyday modern French, it is often omitted, so your sentence without it is completely normal:

• avant que les invités arrivent

Both are possible, but the version without ne is very common in ordinary speech and writing.