Learn Hardcore Portuguese (Portugal): Erros neste exame são frequentes.

That sounds slightly more specific, as if you’re talking about the mistakes that appear in this exam (this particular exam paper, or this type of exam). Both are grammatically correct; the version without the article is a bit more neutral/generic here and very natural in European Portuguese.

What exactly does neste mean, and how is it formed?

Neste is a contraction of the preposition em (in/on/at) + the demonstrative este (this):

em + este → neste (masculine singular)
em + esta → nesta (feminine singular)
em + estes → nestes (masculine plural)
em + estas → nestas (feminine plural)

So neste exame literally means “in this exam”.

Because exame is masculine singular, you use neste, not nesta or nesse.

What’s the difference between neste exame and nesse exame?

Both mean roughly “in this/that exam”, but the nuance is:

este / neste: close to the speaker (or something being focused on right now)
esse / nesse: close to the listener, or something just mentioned, a bit more “distanced”

In practice:

neste exame – the exam I’m doing now / the one I’m focusing on as I speak.
nesse exame – the exam you did / the one we just mentioned (not “right here” in my hands, so to speak).

In many real situations, both are understood, but European Portuguese keeps this proximity distinction more than English does.

Why is frequentes after exame and not before, like in English “frequent errors”?

In Portuguese, adjectives usually come after the noun:

erros frequentes = frequent errors
livros interessantes = interesting books
uma pessoa simpática = a nice person

You can put some adjectives before the noun, but that often adds a nuance (more subjective, emotional, or stylistic). For frequentes, the usual, neutral order is after the noun: erros frequentes.

Frequentes erros is technically possible, but sounds unusual or poetic; in standard speech/writing, say erros frequentes.

Why is it frequentes (plural) and not frequente (singular)?

Adjectives in Portuguese agree in number (singular/plural) and gender with the noun they describe.

erros – masculine plural
So the adjective must also be masculine plural → frequentes

Examples:

um erro frequente – a frequent mistake (masc. singular)
dois erros frequentes – two frequent mistakes (masc. plural)
uma pergunta frequente – a frequent question (fem. singular)
perguntas frequentes – frequent questions (fem. plural)

So here: Erros … são frequentes. → frequentes matches erros.

Why is it são and not estão? In English we just say “are”.

Portuguese distinguishes ser and estar, both translated as “to be”:

ser – inherent, general, characteristic, habitual
estar – temporary state, condition, location

In Erros neste exame são frequentes, we’re talking about a general, habitual characteristic of this exam: errors are generally frequent.

So you use ser → são.

Estar would sound wrong here, as if “right now, at this moment, they are frequent”, which doesn’t match the intended meaning of a recurring pattern.

Could I say Erros são frequentes neste exame instead? Is the word order important?

Yes, Erros são frequentes neste exame is perfectly grammatical and natural.

The difference is only in emphasis:

Erros neste exame são frequentes.
Slightly more focus on “in this exam” as a context where errors occur.
Erros são frequentes neste exame.
Slightly more focus on “errors are frequent”, then you add “in this exam”.

In everyday speech, both are fine; there’s no change in meaning for most contexts.

Could I say Erros neste exame acontecem frequentemente instead of são frequentes?

Yes, you can. They’re close in meaning but not identical in structure:

Erros neste exame são frequentes.
Literally: “Errors in this exam are frequent.” (frequentes is an adjective.)
Erros neste exame acontecem frequentemente.
Literally: “Errors in this exam happen frequently.” (frequentemente is an adverb.)

Both say that errors occur a lot. The first one describes errors as a frequent type of thing; the second focuses more on the event of errors happening.

Both are idiomatic and natural in European Portuguese.

What’s the difference between frequente and frequentemente?

frequente – adjective: “frequent”
- um erro frequente – a frequent error
frequentemente – adverb: “frequently, often”
- Erros acontecem frequentemente. – Errors happen frequently.

In the original sentence, you need an adjective agreeing with erros, so frequentes, not frequentemente.

Could I say É frequente haver erros neste exame? Is that more natural?

Yes, É frequente haver erros neste exame is very natural and often used.

Meaning:

É frequente haver erros neste exame.
= It is common for there to be errors in this exam.

Nuance:

Erros neste exame são frequentes.
Focuses on errors as being frequent.
É frequente haver erros neste exame.
More impersonal: “It is frequent/common that there are errors in this exam.”

In European Portuguese, both are perfectly idiomatic. The impersonal é frequente haver… is very common in written language and more formal speech.

How do I pronounce neste exame são frequentes in European Portuguese?

Very roughly in English-like sounds (European Portuguese):

neste ≈ “NESHT” (final e very short, almost like “nesht(uh)”)
exame ≈ “eh-ZAH-m(uh)” (last e very reduced)
são ≈ nasal like “sowng” (but without a strong final “g”)
frequentes ≈ “fre-KWEN-tesh”

Linked together in normal speech:

neste exame são frequentes → nesht(e) zahm sowng fre-KWEN-tesh

The final -s in frequentes is pronounced like English “sh” in European Portuguese.

Is exame always “exam”, or could it mean something else?

Exame usually means:

A test/exam (school, university, certification)
- Tenho um exame amanhã. – I have an exam tomorrow.
A medical examination/test
- exame de sangue – blood test
- exame médico – medical exam

In Erros neste exame são frequentes, context will decide whether it’s a school exam or, for example, a particular type of medical test. Grammatically it’s the same.