Clorul și amoniacul apar în apă.

In Romanian, the definite article is usually attached to the end of the noun, not placed in front of it.

• clorul = the chlorine
• amoniacul = the ammonia

But there is another important point: in general or scientific statements, Romanian often uses the definite form where English uses no article at all. So clorul here can mean chlorine in a general sense, not only the chlorine in a very specific sense.

Also, when two definite nouns are joined by și, each noun normally keeps its own article: clorul și amoniacul.

-ul is the definite article for many singular masculine and neuter nouns.

So:

• clor → clorul
• amoniac → amoniacul

English puts the before the noun; Romanian often adds the article to the end of the noun instead.

Because the subject is plural in meaning: clorul și amoniacul = two things together.

• apare = he/she/it appears
• apar = they appear

So the verb agrees with the compound subject and takes the plural form.

The dictionary form is a apărea.

This is a good example of a verb whose present-tense forms do not all look exactly like the infinitive. So it is best to learn it as a set:

• eu apar
• tu apari
• el/ea apare
• noi apărem
• voi apăreți
• ei/ele apar

So apar is completely normal here.

Not necessarily in the dramatic English sense of suddenly appear.

In a sentence like this, a apărea can mean something like:

• to occur
• to be present
• to be found

So the verb is often more neutral than English appear may sound.

Because în apă refers to water in a general sense, as a substance.

• în apă = in water
• în apa = in the water (a specific water already identified)

Romanian often leaves a mass noun like apă indefinite after a preposition when speaking generally.

A few important ones:

• ș in și sounds like English sh
• și is roughly shee
• ă in apă sounds like the final vowel in English sofa
• î in în has no exact English equivalent; an approximate version is a short central uh sound said without rounding the lips

A rough pronunciation of the whole sentence would be something like:

KLO-rul shi a-mo-ni-A-kul a-PAR uhn A-puh

That is only approximate, but it is a useful start.

Yes. In standard Romanian, they matter a lot.

For example:

• apă = water
• apa = the water

So the marks are not just optional accents; they can change the form and meaning of a word. For a learner, it is best to keep them.

The order in the sentence is the most neutral one:

Clorul și amoniacul + apar + în apă

Romanian word order is fairly flexible, though. You could also say:

În apă apar clorul și amoniacul.

That version gives more emphasis to în apă. The basic meaning stays the same.

și is the normal Romanian word for and.

It simply connects the two nouns:

• clorul
• amoniacul

So clorul și amoniacul means chlorine and ammonia.

They are usually treated as neuter nouns.

In Romanian, neuter nouns behave like masculine nouns in the singular and like feminine nouns in the plural. In this sentence, that matters mainly because the singular definite form looks like a masculine one:

• clorul
• amoniacul

For this sentence, the most useful thing is simply to learn these singular forms as they appear here.