A conta bancária está na declaração pré-preenchida.

In Portuguese, it is very common to use the definite article when talking about a specific thing already understood in context.

So a conta bancária means the bank account.

• a = the for a feminine singular noun
• conta = account
• bancária = bank / banking

Portuguese uses articles more often than English does, so leaving out a would often sound less natural here.

The noun conta is a feminine noun in Portuguese, so the words that go with it must match that gender.

That is why you get:

• a conta
• conta bancária

The adjective bancária changes to feminine singular to agree with conta.

Compare:

• o cartão bancário = the bank card
• a conta bancária = the bank account

Portuguese has two main verbs for to be: ser and estar.

Here, está is used because the sentence talks about location: the bank account is in the pre-filled declaration.

A useful rule:

• ser = identity, definition, permanent characteristics
• estar = location, condition, temporary states

So:

• A conta bancária está na declaração... = The bank account is in the declaration.
• A conta bancária é importante. = The bank account is important.

Na is a contraction of:

• em = in / on / at
• a = the

So:

• em + a = na

That means na declaração = in the declaration.

Other common contractions:

• no = em + o
• nos = em + os
• nas = em + as

Because declaração is a feminine noun.

So the article is a, not o:

• a declaração = the declaration

When combined with em, you get:

• em + a declaração
• na declaração

If it were a masculine noun, you would use no instead.

Declaração means declaration, and in Brazilian usage it often refers to an official filing, especially a tax return depending on context.

Pré-preenchida means pre-filled or already filled in beforehand.

So declaração pré-preenchida is a pre-filled declaration, often something like a pre-filled tax return form.

In Brazil, this is a very common expression in tax and government-related contexts.

Because pré- is a prefix meaning pre- / before, and in this kind of formation Portuguese commonly uses a hyphen.

So:

• pré = before
• preenchida = filled in

Together:

• pré-preenchida = pre-filled

This is a spelling convention, not a special grammar feature of the sentence itself.

It agrees with declaração, which is feminine singular.

So the adjective must also be feminine singular:

• declaração pré-preenchida

Compare:

• documento pré-preenchido = masculine singular
• declaração pré-preenchida = feminine singular
• documentos pré-preenchidos = masculine plural
• declarações pré-preenchidas = feminine plural

In Portuguese, adjectives often come after the noun.

So these are very normal patterns:

• conta bancária
• declaração pré-preenchida

English often puts adjectives before the noun, but Portuguese frequently places them after.

That said, adjective position in Portuguese can sometimes change emphasis or meaning, but in this sentence the post-noun position is the natural one.

Está is pronounced roughly like es-TAH, with the stress on the second syllable.

A few points:

• the e at the beginning is pronounced
• the tá is stressed because of the accent mark
• the final a is an open vowel

The accent in está shows the stressed syllable.

A rough pronunciation is deh-kla-ra-SOWN, with stress on the last syllable.

Important details:

• ção is a very common ending in Portuguese
• it sounds roughly like sown or sahng, depending on accent and how closely you imitate Brazilian pronunciation
• the ç makes an s sound, never a k sound

So declaração does not sound like English declaration even though the words are related.

A rough pronunciation is ban-KAH-rya, with stress on KAH.

The written accent in bancária marks the stressed syllable:

• ban-CÁ-ria

Also, the final ria is usually pronounced smoothly together, not as three fully separate English-like syllables.

Grammatically, people will understand it, but standard Portuguese contracts em + a into na.

So the natural, correct form is:

• A conta bancária está na declaração pré-preenchida.

Using em a instead of na sounds unnatural and non-native.

You would change all the parts that need to agree in number.

For example:

• As contas bancárias estão nas declarações pré-preenchidas.

Changes:

• a → as
• conta → contas
• bancária → bancárias
• está → estão
• na → nas
• declaração → declarações
• pré-preenchida → pré-preenchidas

This is a good example of how agreement works across the sentence in Portuguese.