A avaria e o prejuízo são grandes.

Because the subject is compound: A avaria e o prejuízo = two things joined by e (and).

In Portuguese, when two singular nouns are joined by e, the verb normally goes in the plural:

• A avaria e o prejuízo são grandes.
• O carro e a moto são novos.

So é would be wrong here in standard Portuguese, because that would be singular.

Those are the definite articles in Portuguese:

• a = the for a singular feminine noun
• o = the for a singular masculine noun

So:

• a avaria
• o prejuízo

English uses just one word, the, but Portuguese articles change according to gender and number.

In Portuguese, it is very common and natural to repeat the article before each noun:

• A avaria e o prejuízo...

That sounds complete and standard.

You may sometimes hear article omission in certain contexts, but in a sentence like this, repeating the article is the most natural choice. For a learner, it is best to copy this pattern.

Because the adjective must agree with what it describes.

Here, grandes describes both nouns together:

• a avaria
• o prejuízo

Since the two nouns together form a plural idea, the adjective becomes plural:

• singular: grande
• plural: grandes

So:

• A avaria é grande.
• O prejuízo é grande.
• A avaria e o prejuízo são grandes.

Some Portuguese adjectives have different masculine and feminine forms, but grande is one of the adjectives that has the same form for masculine and feminine in the singular:

• o problema grande
• a avaria grande

In the plural, it becomes:

• grandes

So with mixed gender nouns like a avaria + o prejuízo, the plural adjective is simply grandes.

Avaria usually refers to damage, a defect, a malfunction, or a breakdown, depending on context.

Common uses:

• damage to goods or property
• a mechanical or technical problem
• a breakdown in a vehicle or machine

So it is a somewhat formal/useful noun for physical or technical damage.

Prejuízo usually means loss, especially a financial loss, damage, or harm.

Very often it suggests that someone suffered a negative consequence, especially in money or business terms.

So in this sentence, it likely refers to the loss caused by the damage/breakdown.

Not exactly.

A simple way to see the difference:

• avaria = the damage/problem/breakdown itself
• prejuízo = the loss or negative consequence caused by it

For example, a machine may have an avaria, and that can cause a financial prejuízo.

So the sentence mentions both the physical/technical problem and the resulting loss.

Because Portuguese nouns have grammatical gender.

In this case:

• avaria is feminine → a avaria
• prejuízo is masculine → o prejuízo

Often nouns ending in -a are feminine and nouns ending in -o are masculine, though that is a pattern, not an absolute rule.

You generally need to learn the noun together with its article:

• a avaria
• o prejuízo

A simple pronunciation guide:

• avaria → ah-vah-REE-ah
• prejuízo → preh-joo-EE-zoo
• são → sounds roughly like sowng, with a nasal sound

A few helpful notes:

• In prejuízo, the accent mark shows the stress: -uí-
• são is nasal, so it does not sound like plain sao
• In Brazilian Portuguese, the r in avaria is usually a soft sound in this position

In standard Portuguese, no.

Because the subject has two nouns, you need:

• plural verb: são
• plural adjective: grandes

So the correct form is:

• A avaria e o prejuízo são grandes.

Using é grande would only work with a singular subject:

• A avaria é grande.
• O prejuízo é grande.

Yes, but the original order is the most neutral and natural.

Possible variation:

• Grandes são a avaria e o prejuízo.

This is grammatically possible, but it sounds more literary or emphatic.

For normal usage, the most straightforward order is:

• A avaria e o prejuízo são grandes.

It sounds somewhat neutral to formal, mainly because of the word avaria, which is a bit more technical or formal than some everyday alternatives.

In more casual speech, depending on context, a Brazilian speaker might choose other words, but the sentence itself is perfectly natural and correct.

Yes, very possibly.

In Portuguese, grande/grandes can mean not only big/large, but also serious, considerable, or significant, depending on context.

So in this sentence, são grandes may suggest:

• the damage is extensive
• the loss is considerable
• the situation is serious

That kind of broader meaning is very common.