Ο αριθμός πρωτοκόλλου είναι απαραίτητος για την εξέταση της ένστασης.

Because Greek often uses the genitive where English uses of or a noun used attributively.

So αριθμός πρωτοκόλλου is literally something like number of protocol/registration, and in normal administrative English this corresponds to a reference number, file number, or protocol number.

This pattern is very common in Greek:

• αριθμός τηλεφώνου = telephone number
• κέντρο πόλης = city center
• έκδοση βιβλίου = edition of a book / book edition

So πρωτοκόλλου depends on αριθμός and tells you what kind of number it is.

In Ο αριθμός πρωτοκόλλου, the main noun is αριθμός, so it takes the article: ο αριθμός.

The word πρωτοκόλλου is attached to it as a genitive complement, and Greek often leaves that second noun without an article in this kind of fixed administrative expression.

So:

• ο αριθμός πρωτοκόλλου = the protocol/reference number

You could sometimes see a genitive noun with an article in other contexts, but here the article is not needed. The phrase works as a standard compound-like expression.

Because it agrees with ο αριθμός, which is a masculine singular noun.

In Greek, adjectives must agree with the noun they describe in:

• gender
• number
• case

So here:

• ο αριθμός = masculine singular nominative
• απαραίτητος = masculine singular nominative

If the noun were feminine or neuter, the adjective would change too:

• Η αίτηση είναι απαραίτητη.
• Το έγγραφο είναι απαραίτητο.

So απαραίτητος is masculine simply because αριθμός is masculine.

είναι is the present tense of to be: is.

In this sentence it links the subject and the adjective:

• Ο αριθμός πρωτοκόλλου = subject
• είναι = is
• απαραίτητος = necessary

So the structure is very straightforward: X is necessary.

Greek sometimes omits είναι in very informal contexts, headlines, notes, or special styles, but in a normal full sentence like this, είναι is the standard and expected form.

The preposition για normally takes the accusative.

That is why you get:

• για την εξέταση

Here:

• την = feminine singular accusative article
• εξέταση = feminine singular accusative noun

So after για, Greek uses the accusative to mean things like:

• for
• for the purpose of
• regarding, depending on context

In this sentence, για την εξέταση means for the examination/consideration.

Because ένστασης depends on εξέταση.

The phrase is:

• η εξέταση της ένστασης

This means literally the examination of the objection/appeal.

So:

• η εξέταση = the examination
• της ένστασης = of the objection

Greek uses the genitive here because ένσταση is the thing being examined, and Greek expresses that relationship with of + genitive.

If you said την ένσταση, that would be accusative, and it would not fit this noun phrase.

The dictionary forms are:

• αριθμός → appears here as αριθμός
• πρωτόκολλο → appears here as πρωτοκόλλου
• απαραίτητος → appears here as απαραίτητος
• εξέταση → appears here as εξέταση
• ένσταση → appears here as ένστασης

So the forms that may look less familiar to a learner are:

• πρωτοκόλλου = genitive singular of πρωτόκολλο
• ένστασης = genitive singular of ένσταση

This is a very useful habit in Greek: when you meet a form in a sentence, try to identify its dictionary form and its case.

Yes. Greek word order is more flexible than English word order because case endings already show the grammatical relationships.

The original sentence is neutral and natural:

• Ο αριθμός πρωτοκόλλου είναι απαραίτητος για την εξέταση της ένστασης.

But you could also say:

• Για την εξέταση της ένστασης, ο αριθμός πρωτοκόλλου είναι απαραίτητος.

This puts more emphasis on the purpose or context first.

Even so, not every order sounds equally natural in every situation. The original version is the most standard, especially in formal or administrative language.

In real administrative Greek, αριθμός πρωτοκόλλου is a very common official term. It usually refers to the registration number given to a document when it is officially filed or received.

So although the literal pieces are easy to analyze, the phrase often functions as a set expression meaning something like:

• reference number
• registration number
• filing number
• protocol number

The exact English choice depends on the institution and context.

Because the article changes to match the noun’s gender, number, and case.

Here you have:

• ο αριθμός
  masculine singular nominative

• την εξέταση
  feminine singular accusative

• της ένστασης
  feminine singular genitive

So Greek articles are not fixed the way English the is. They change form depending on the grammar of the sentence.

This is one of the biggest differences for English speakers learning Greek.

A rough pronunciation guide is:

O arith-MOS proto-KOL-lou EE-ne a-pa-RE-ti-tos ya tin ek-SE-ta-si tis EN-sta-sis.

A few helpful notes:

• θ in αριθμός sounds like th in think
• για sounds like ya
• αι in απαραίτητος sounds like e
• the stressed syllables are marked by the written accents:
  • αριθμός
  • πρωτοκόλλου
  • απαραίτητος
  • εξέταση
  • ένστασης

Paying attention to stress is very important in Greek, because it is always pronounced.