Wenn ich nervös bin, ist mein Mund trocken.

Because wenn is a subordinating conjunction. In German, a clause introduced by a subordinating conjunction usually sends the conjugated verb to the end of that clause.

So:

• ich bin nervös = normal main clause
• wenn ich nervös bin = subordinate clause, so bin moves to the end

This is one of the most important German word-order patterns to learn.

In German main clauses, the conjugated verb normally comes in second position.

Here, the whole clause Wenn ich nervös bin comes first. That entire clause counts as position 1, so the verb in the main clause must come immediately after it:

• Wenn ich nervös bin, ist mein Mund trocken.

If you start with the main clause instead, then the normal order is:

• Mein Mund ist trocken, wenn ich nervös bin.

Both are correct. The original sentence just puts the wenn-clause first.

Here, wenn means when or whenever, and sometimes it can feel close to if, depending on context.

In this sentence, it suggests a repeated or general situation:

• whenever I am nervous
• when I am nervous

A useful guideline:

• wenn = when/whenever/if for repeated, general, or possible situations
• als = when for a single event in the past

So if you are describing a general pattern, wenn is the right choice.

Yes, absolutely.

These two versions are both correct:

• Wenn ich nervös bin, ist mein Mund trocken.
• Mein Mund ist trocken, wenn ich nervös bin.

The difference is mainly emphasis and flow:

• starting with Wenn ich nervös bin emphasizes the condition first
• starting with Mein Mund ist trocken emphasizes the result first

Because Mund is the subject of the main clause, so it is in the nominative case.

In:

• ist mein Mund trocken

the subject is mein Mund, and ist agrees with it.

You would use meinen Mund only in the accusative, for example:

• Ich öffne meinen Mund.

So here:

• mein Mund = nominative
• meinen Mund = accusative

Because trocken is a predicate adjective here. After verbs like sein, werden, and bleiben, adjectives usually do not take adjective endings.

So:

• Mein Mund ist trocken.
• Ich bin nervös.
• Das Wetter wird kalt.

But when an adjective comes before a noun, it does take an ending:

• ein trockener Mund
• mein trockener Mund

That is the difference:

• after sein: trocken
• before a noun: trockener

Because German uses commas to separate subordinate clauses from main clauses.

Since Wenn ich nervös bin is a subordinate clause and it comes first, it must be followed by a comma:

• Wenn ich nervös bin, ist mein Mund trocken.

This is a standard rule in German punctuation.

Mostly yes. nervös is a very common adjective and works much like English nervous:

• Ich bin nervös.
• Sie ist vor der Prüfung nervös.

A pronunciation note: nervös has an ö, which does not sound like a normal English o. The stress is on the second syllable: nehr-VÖS.

Bin is the first-person singular present tense form of sein:

• ich bin = I am
• du bist = you are
• er/sie/es ist = he/she/it is

That is why the sentence has:

• ich nervös bin in the subordinate clause
• mein Mund ... ist in the main clause

The verb changes depending on the subject.

Because mein is already functioning as a determiner. It takes the place where an article would normally go.

So you say:

• mein Mund
• not der mein Mund

Compare:

• der Mund = the mouth
• mein Mund = my mouth

You use one determiner there, not both together.

Yes. Mund is the standard German word for mouth.

In this sentence, mein Mund ist trocken is a natural way to express the idea of having a dry mouth.

You may also hear related expressions such as:

• einen trockenen Mund haben = to have a dry mouth
• Der Mund ist trocken = the mouth is dry

Yes, depending on context, wenn can sometimes be understood as either when or if.

In this sentence, the most natural sense is usually a general one:

• whenever I am nervous, my mouth is dry

But in some contexts, a listener could also understand it as:

• if I get nervous, my mouth becomes dry

So wenn is flexible, and context tells you whether it feels more like when, whenever, or if.