Ο υπεύθυνος ορόφου ελέγχει τον πυροσβεστήρα.

Originally, υπεύθυνος is an adjective meaning responsible. But in this sentence it is being used like a noun, meaning the person in charge / the supervisor / the manager.

This is very common in Greek: an adjective can function as a noun when the context makes the person or thing clear.

So here:

• ο υπεύθυνος = the person in charge / the supervisor

If the person were female, Greek would use the feminine form:

• η υπεύθυνη

The sentence contains three noun forms with three different functions:

• ο υπεύθυνος — nominative
  This is the subject, the person doing the action.

• ορόφου — genitive
  This means of the floor, showing what the supervisor is responsible for.

• τον πυροσβεστήρα — accusative
  This is the direct object, the thing being checked.

So the structure is basically:

• [subject] [verb] [object]
• with ορόφου attached to υπεύθυνος to specify what kind of supervisor

Because Greek often uses the genitive to express relationships like of, especially with roles, responsibilities, and possession.

So:

• ορόφου = of the floor

This is similar to expressions like:

• διευθυντής σχολείου = school principal
  literally principal of a school / of the school
• υπεύθυνος ασφαλείας = safety officer
  literally person responsible for safety

In your sentence, υπεύθυνος ορόφου means something like:

• floor supervisor
• literally supervisor/person in charge of the floor

Because Greek often leaves out the article in this kind of title + genitive expression.

So:

• ο υπεύθυνος ορόφου is a compact expression, almost like a job title: floor supervisor

Greek often does this with professions, roles, and set expressions.

That said, you can also say:

• ο υπεύθυνος του ορόφου

This is also grammatical and may sound more explicit: the person responsible for the floor.

Very roughly:

• ο υπεύθυνος ορόφου = more title-like, compact
• ο υπεύθυνος του ορόφου = more explicitly the supervisor of the floor

Because it is a masculine singular noun in the accusative case, and Greek normally uses the definite article with definite direct objects.

Here:

• ο πυροσβεστήρας = nominative singular
• τον πυροσβεστήρα = accusative singular

The article changes too:

• ο → nominative masculine singular
• τον → accusative masculine singular

So τον πυροσβεστήρα means the fire extinguisher as the object of the verb.

ελέγχει is:

• 3rd person singular
• present tense
• active voice
• from the verb ελέγχω = to check / inspect / control

So it means:

• he/she checks
• is checking

In Greek, the present tense can express either a general action or something happening now, depending on context.

A few related forms:

• εγώ ελέγχω = I check
• εσύ ελέγχεις = you check
• αυτός/αυτή ελέγχει = he/she checks

No. Greek word order is more flexible than English word order because case endings and articles help show each word’s function.

The sentence as given:

• Ο υπεύθυνος ορόφου ελέγχει τον πυροσβεστήρα.

is a neutral, standard order: subject + verb + object.

But Greek can also change the order for emphasis, for example:

• Τον πυροσβεστήρα ελέγχει ο υπεύθυνος ορόφου.
  This puts more focus on the fire extinguisher.

Even though the order changes, the cases still show who is doing what.

A rough English-friendly guide:

• Ο υπεύθυνος ≈ o i-PEF-thi-nos
• ορόφου ≈ o-RO-fou
• ελέγχει ≈ e-LE-ghi
• τον πυροσβεστήρα ≈ ton pi-ro-sve-STI-ra

A few useful pronunciation notes:

• ευ is pronounced ef before a voiceless sound, so in υπεύθυνος it sounds like ef
• θ is like th in think
• χ is not English ch; it is a throat sound, somewhat like German Bach or a soft h/kh
• The written accent mark shows where the stress goes:
  • υπεύθυνος
  • ορόφου
  • ελέγχει
  • πυροσβεστήρα

No, and learners often mix them up.

• πυροσβεστήρας = fire extinguisher
• πυροσβέστης = firefighter

They are related words, but they mean different things.

So in your sentence, τον πυροσβεστήρα is definitely the fire extinguisher, not the firefighter.

You would change the subject article and the noun/adjective form:

• Η υπεύθυνη ορόφου ελέγχει τον πυροσβεστήρα.

Changes:

• ο → η
• υπεύθυνος → υπεύθυνη

The verb ελέγχει stays the same, because Greek uses the same 3rd person singular verb form for he and she.

Yes. It works very much like a role label or job title.

Greek often builds these compact expressions with:

• a main noun or adjective used as a noun
• plus a genitive noun

So υπεύθυνος ορόφου is not just any random combination of words; it feels like a normal institutional phrase, similar to:

• υπεύθυνος καταστήματος = store manager
• υπεύθυνος ασφαλείας = safety officer
• υπεύθυνος βάρδιας = shift supervisor

That is why the sentence sounds natural and efficient in Greek.