Das Risiko ist groß.

Because Risiko is a neuter noun in German, and the definite article for a neuter singular noun in the nominative case is das.

German noun genders are:

• der = masculine
• die = feminine
• das = neuter

So:

• das Risiko = the risk

It is in the nominative case because it is the subject of the sentence.

In Das Risiko ist groß, the thing being talked about is das Risiko, so it is the subject:

• Das Risiko = subject
• ist = is
• groß = large/great

Because in a normal German main clause, the conjugated verb usually comes in second position.

So the structure is:

• Das Risiko = first element
• ist = verb in second position
• groß = rest of the sentence

This is a basic German word order rule:

• Das Risiko ist groß.
• Der Mann ist müde.
• Das Haus ist alt.

Because groß is being used as a predicate adjective, not an adjective directly before a noun.

Compare:

• Das Risiko ist groß.
  Here groß comes after ist, so it does not take an ending.

• Das große Risiko
  Here groß comes before the noun Risiko, so it does take an adjective ending: große.

This is a very important difference in German:

• before a noun → adjective ending needed
• after sein/werden/bleiben → no ending

Ist is the 3rd person singular form of the verb sein (to be).

The present tense forms are:

• ich bin
• du bist
• er/sie/es ist
• wir sind
• ihr seid
• sie/Sie sind

Since das Risiko is singular, German uses ist.

Yes, groß literally means big or large, but in this sentence it often corresponds more naturally to English great or high, depending on context.

So Das Risiko ist groß can mean:

• the risk is big
• the risk is great
• the risk is high

German often uses groß in a wider way than English uses big.

Yes, absolutely. Das Risiko ist hoch is also very common.

Both are possible, but they can feel slightly different:

• groß = big/great
• hoch = high

In many contexts, English prefers high risk, so Das Risiko ist hoch may sound especially natural as a translation of The risk is high.

In German, all nouns are capitalized, but adjectives are usually not.

So:

• Risiko is a noun → capitalized
• groß is an adjective → not capitalized

Das is capitalized here because it is the first word of the sentence. If it appeared in the middle of a sentence, it would normally be written das.

groß is pronounced approximately like grohs.

A few notes:

• ö is a special German vowel sound, not the same as English o
• ß is pronounced like s

So:

• groß sounds like grohs
• not like English gross

Both represent an s sound, but German spelling uses them differently.

In standard German spelling:

• ß usually comes after a long vowel or diphthong
• ss usually comes after a short vowel

So:

• groß has ß
• muss has ss

In Switzerland, people usually write ss instead of ß, so you may see gross there.

Yes, das can mean different things depending on context. It can be:

• the neuter article the
• the demonstrative that
• the relative pronoun that/which

In Das Risiko ist groß, it is simply the definite article:

• das Risiko = the risk

So here it does not mean that.

It is neutral and works in both formal and informal German.

There is nothing especially casual or especially formal about it. It is just a standard sentence:

• Das Risiko ist groß.

Usually, no. In normal German, you would normally say Das Risiko ist groß if you mean the risk is great.

Leaving out the article sounds unnatural in most ordinary contexts.

You might omit an article only in special cases, such as headings, notes, or very abstract style, but for normal sentence building, use:

• Das Risiko ist groß.

The pattern is:

subject + form of sein + adjective

So:

• Das Risiko = subject
• ist = form of sein
• groß = predicate adjective

This same pattern is extremely common in German:

• Das Kind ist klein.
• Der Kaffee ist heiß.
• Die Aufgabe ist schwer.

So this sentence is a very useful model to remember.