O ouro é caro.

O is the masculine singular definite article, equivalent to the.

In Portuguese, general statements about materials, substances, and whole categories often use the definite article. So o ouro is the natural way to say gold in a general sense.

That is different from English, which often uses no article in these cases.

Examples:

• O ouro é caro.
• A prata é bonita.
• O café está quente.

Yes. Ouro is a masculine noun, so it takes:

• o as its article
• masculine adjectives, such as caro

That is why the sentence is:

• O ouro é caro.

not:

• A ouro é cara.

É is from ser, which is used for general characteristics, definitions, and more permanent or inherent qualities.

Here, the sentence is expressing a general fact about gold: it is expensive. That is why ser is the normal choice.

So:

• O ouro é caro. = a general truth / characteristic

If you used está caro, that would sound more like it is expensive right now or it has become expensive, often in a temporary or current-market sense.

Compare:

• O ouro é caro. = Gold is expensive.
• O ouro está caro. = Gold is expensive right now.

In Portuguese, adjectives often come after the noun.

So:

• ouro caro = expensive gold

In this sentence, the structure is:

• O ouro = the subject
• é = is
• caro = expensive

This is very normal word order in Portuguese.

Because ouro is singular.

Adjectives in Portuguese usually agree with the noun in gender and number:

• masculine singular: caro
• feminine singular: cara
• masculine plural: caros
• feminine plural: caras

Examples:

• O ouro é caro.
• A prata é cara.
• Os metais são caros.
• As joias são caras.

In standard Portuguese, o ouro é caro is the normal and most natural form for a general statement.

Leaving out the article here sounds unnatural in most situations.

So for a learner, the safe choice is:

• O ouro é caro.

In Brazilian Portuguese, ouro is usually pronounced roughly like OH-roh, but the first part is a diphthong, something like ou in Portuguese, not exactly like English oh.

A rough guide:

• ou = a sound similar to o in English go
• r = often a soft flap between vowels in many accents
• final o = usually sounds like u or a weak o in many Brazilian accents

So a rough approximation is:

• OH-ru

But pronunciation varies by region.

É is pronounced like eh, similar to the e in English bet, but clearer and more open.

The accent mark is important because it shows both pronunciation and meaning:

• é = is
• e = and

So:

• é = verb
• e = conjunction

The accent in é serves two purposes:

1. It shows the stressed vowel sound.
2. It distinguishes é (is) from e (and).

This is a very common and important distinction in Portuguese.

Examples:

• Ele é rico. = He is rich.
• Ouro e prata. = Gold and silver.

Mostly, caro means expensive, but it can also mean dear in formal or affectionate language.

Examples:

• Este carro é caro. = This car is expensive.
• Meu caro amigo... = My dear friend...

In O ouro é caro, the meaning is clearly expensive.

Yes. You can intensify the adjective with muito:

• O ouro é muito caro. = Gold is very expensive.

This is a very common pattern:

• A casa é grande.
• A casa é muito grande.

Usually caro focuses on cost or high price, so expensive is the most direct meaning.

If you specifically want to say valuable, Portuguese often uses words like:

• valioso
• precioso

Examples:

• O ouro é valioso.
• O ouro é precioso.

So caro is more about price than abstract value.

The pattern is:

article + noun + form of ser + adjective

So here:

• O = the
• ouro = noun
• é = is
• caro = adjective

This is one of the most useful basic sentence patterns in Portuguese.

More examples:

• O café é forte.
• A água é fria.
• O carro é novo.