A prestação de contas mostra a inadimplência.

Because both nouns are feminine singular:

• a prestação
• a inadimplência

In Portuguese, nouns usually take an article more often than in English, especially in full written sentences. So a here means the.

This sentence structure is:

• A prestação de contas = the accounting/reporting/account statement
• mostra = shows
• a inadimplência = the delinquency/default/non-payment

So the two a words are just the normal feminine singular definite article.

Prestação de contas is a set phrase in Portuguese. It is often used in formal, administrative, legal, financial, or institutional contexts.

Depending on context, it can mean things like:

• accounting/reporting
• rendering of accounts
• financial statement/report
• accountability report

Literally, it is related to the idea of giving an account of something or showing the financial records/results.

So even if the literal pieces are understandable, the full expression works as a fixed phrase, not just a random combination of words.

Because the subject is singular:

• A prestação de contas = singular
• so the verb must also be singular: mostra

Even though de contas contains the plural noun contas, that does not make the whole subject plural.

The main noun is prestação, and that is singular.

So:

• A prestação de contas mostra... = correct
• A prestação de contas mostram... = incorrect

This is a very common point for English speakers, because the plural noun inside the phrase can be distracting.

Here, de links the nouns and means something like of.

• prestação = rendering/providing/presentation
• de contas = of accounts

So literally it is something like rendering of accounts.

Portuguese often uses de + noun where English might use:

• of
• a possessive structure
• or a more natural compound noun

For example:

• prestação de serviços = provision of services
• plano de saúde = health plan
• sala de aula = classroom

So prestação de contas is a normal noun phrase pattern in Portuguese.

Inadimplência is a fairly formal word. It is common in:

• banking
• contracts
• billing
• accounting
• business/legal language

It refers to failure to pay, default, or delinquency in payment.

Related words:

• inadimplente = a person or entity in default / behind on payments
• adimplente = up to date on payments / compliant with payment obligations

In casual everyday speech, people might more often say things involving:

• atraso no pagamento = late payment
• dívida = debt
• não pagou = didn’t pay

So inadimplência is very natural in formal financial language, but more technical than everyday conversation.

Yes, in some contexts Portuguese can omit the article with abstract nouns, but here a inadimplência sounds very natural because it refers to the delinquency/default shown by that report.

Portuguese often uses definite articles with abstract nouns more freely than English does.

So:

• mostra a inadimplência = shows the delinquency/default
• mostra inadimplência = could be possible in some contexts, but it sounds less specific and less natural here

The version with a feels more complete and standard in formal writing.

Yes. The whole expression is grammatically singular because the head noun is prestação.

Think of it this way:

• main noun: prestação = singular
• complement: de contas = of accounts

This is similar to how a phrase in English can still be singular even if it contains a plural noun, such as the list of items is...

So in Portuguese:

• A prestação de contas é clara.
• A prestação de contas mostra...

Both use singular agreement.

Yes, it sounds formal and technical.

It fits contexts like:

• business reports
• financial analysis
• internal company documents
• banking statements
• legal or administrative writing

In ordinary conversation, a Brazilian might say something simpler, depending on the exact meaning, for example:

• O relatório mostra que tem gente sem pagar.
• O documento mostra atraso nos pagamentos.
• As contas mostram inadimplência.

So the original sentence is correct and natural, but it belongs more to formal written Portuguese than casual speech.

Yes, but the original order is the most neutral and standard:

• A prestação de contas mostra a inadimplência.

You could sometimes change the structure for style or emphasis, for example:

• A inadimplência é mostrada pela prestação de contas.

But that sounds more formal and less direct.

Portuguese usually prefers the straightforward pattern:

• subject + verb + object

So the original sentence is the best default version.

A helpful approximation is:

• a pres-ta-SOWN dji KON-tas

A few pronunciation notes:

• ção in prestação sounds roughly like sown with a nasal ending
• de often sounds like dji before some sounds in Brazilian Portuguese
• contas has a clear kon sound

And inadimplência is approximately:

• ee-na-jeem-PLEN-see-a or ee-na-deem-PLEN-see-a

Depending on accent, the di may sound softer, closer to jee.

The stress is on:

• prestaÇÃO
• inadimPLÊNcia

Yes. They are directly related.

• prestar contas = to render accounts / to account for something / to report formally
• prestação de contas = the act or process of doing that; the report/accounting itself

So:

• A empresa precisa prestar contas. = The company needs to account for its actions/finances.
• A prestação de contas foi enviada. = The accountability/financial report was sent.

This verb-noun relationship is very common in Portuguese and is useful to recognize.