Мне нужно сдать заявление в деканат до обеда.

Because нужно works with the person in the dative case, not the nominative.

So:

• мне = to me / for me
• нужно = necessary / needed

Literally, Мне нужно сдать заявление is something like It is necessary for me to submit the application.

This is a very common Russian pattern:

• Мне нужно уйти = I need to leave
• Тебе нужно позвонить = You need to call
• Нам нужно учиться = We need to study

Here нужно means need to / have to / it is necessary to.

It is often used with an infinitive:

• нужно сделать = need to do
• нужно прийти = need to come
• нужно сдать = need to submit / hand in

It is neutral and very common in everyday Russian. It does not literally mean want. It expresses necessity.

In this sentence, сдать means to hand in, submit, turn in.

This verb has several meanings depending on context, such as:

• сдать экзамен = pass an exam
• сдать квартиру = rent out an apartment
• сдать документы = hand in documents

Here, because the object is заявление and the place is в деканат, the meaning is clearly submit/hand in.

Сдать is the perfective form, while сдавать is imperfective.

In this sentence, the speaker means a single completed action: the application must be submitted. That is why Russian uses сдать.

Compare:

• Мне нужно сдать заявление сегодня.
  = I need to submit the application today.
  (one completed action)

• Я каждый год сдаю документы в деканат.
  = Every year I submit documents to the dean’s office.
  (repeated/habitual action)

So сдать fits because the focus is on getting the submission done.

Заявление is in the accusative case, because it is the direct object of сдать.

However, for neuter inanimate nouns like заявление, the accusative form is the same as the nominative:

• nominative: заявление
• accusative: заявление

So the form does not change, but grammatically it is still accusative.

Заявление usually means a formal written application, request, or statement.

In university or office contexts, it often refers to an official paper you submit for some administrative purpose.

So depending on context, it could be translated as:

• application
• request
• written statement
• form

In this sentence, application is often the most natural translation.

Деканат is the dean’s office or the faculty administration office at a university.

It is not the dean as a person. It refers to the administrative office connected with a faculty/department, where students often submit forms, get documents processed, and deal with official matters.

So в деканат means to the dean’s office.

Because here в expresses direction/movement toward a place, not location.

With в:

• в + accusative = into/to
• в + prepositional = in/inside/at

So:

• сдать заявление в деканат = submit the application to the dean’s office
• Я в деканате = I am in the dean’s office

The sentence involves sending/handing something to that office, so the accusative деканат is used.

До requires the genitive case, so:

• обед = lunch
• до обеда = before lunch

This phrase means before lunchtime / before noon-ish, depending on context.

Other examples:

• до вечера = until evening
• до понедельника = by Monday / until Monday
• до конца недели = before the end of the week

So обеда is genitive singular after до.

It can mean either, depending on context.

Literally, it is before lunch. But in everyday speech, especially in work or school contexts, it often means before lunchtime, which can function a lot like before noon or in the first half of the day.

The exact time depends on the situation.

Russian often leaves out the subject when it is clear from context.

Here, мне already shows who is involved: to me / for me. That makes an explicit я unnecessary.

Russian commonly does this when the meaning is obvious:

• Мне нужно идти. = I need to go.
• Нам надо поговорить. = We need to talk.

So the sentence does not need a separate я.

The structure is:

[person in dative] + [нужно] + [infinitive] + [object] + [destination/place] + [time limit]

In this sentence:

• Мне = person affected, in dative
• нужно = necessary/need to
• сдать = infinitive verb
• заявление = object
• в деканат = destination/recipient place
• до обеда = deadline/time limit

This pattern is very common in Russian.

Yes. Russian word order is flexible, and changing it can shift emphasis.

For example:

• Мне нужно сдать заявление в деканат до обеда.
  Neutral: I need to submit the application to the dean’s office before lunch.

• До обеда мне нужно сдать заявление в деканат.
  Emphasis on the deadline: Before lunch, I need to submit the application...

• Заявление мне нужно сдать в деканат до обеда.
  Emphasis on the document.

The original order sounds natural and neutral.

Yes, often you can, but the nuance is slightly different.

• подать заявление = submit/file an application
• сдать заявление = hand in/turn in an application

In many administrative contexts, both can work.
However:

• подать often sounds a bit more official, like file an application
• сдать often emphasizes physically handing it in

So подать заявление в деканат would also be very natural.

The stress is:

Мне́ ну́жно сдать заявле́ние в декана́т до обе́да.

A rough pronunciation guide:

• Мне = mnye
• нужно = NOOZH-na
• сдать = zdaht’
• заявление = za-yav-LYE-ni-ye
• в деканат = v de-ka-NAT
• до обеда = da a-BYE-da

The biggest stress points to notice are:

• Мне́
• ну́жно
• заявле́ние
• декана́т
• обе́да

It is neutral and perfectly normal in everyday speech.

The vocabulary is a bit administrative because of заявление and деканат, but the grammar itself is standard and common. You could say this in conversation, in a text message, or when explaining what you have to do.

So it is neither especially formal nor especially casual.