הכלב צריך אוויר נקי.

ה־ is the Hebrew definite article, the equivalent of English the.

• כלב = dog
• הכלב = the dog

So the sentence starts with the dog, not just a dog.

A common pronunciation guide is:

ha-KE-lev tsa-RIKH a-VIR na-KI

A few notes:

• כ in הכלב here sounds like k
• צריך ends with a throaty sound, like the ch in Scottish loch or German Bach
• Stress is usually on:
  • KE in kelev
  • RIKH in tsarikh
  • VIR in avir
  • KI in naki

Because צריך has to match the subject in gender and number.

Here the subject is הכלב (the dog), which is masculine singular, so Hebrew uses the masculine singular form:

• צריך = masculine singular
• צריכה = feminine singular
• צריכים = masculine plural
• צריכות = feminine plural

So with הכלב, צריך is the correct form.

In everyday Modern Hebrew, you can treat צריך as the normal present-tense way to say need.

So:

• הכלב צריך אוויר נקי = The dog needs clean air

Grammatically, צריך behaves a bit like an adjective, which is why it changes for gender and number. That is also why there is no separate word for is in the sentence. Literally, it is something like the dog [is] needing clean air.

Because את is used before a definite direct object, and אוויר נקי here is indefinite.

• אוויר נקי = clean air
• האוויר הנקי = the clean air

So:

• הכלב צריך אוויר נקי = The dog needs clean air
• הכלב צריך את האוויר הנקי = The dog needs the clean air

In your sentence, the object is not definite, so there is no את.

Because in Hebrew, adjectives usually come after the noun they describe.

So:

• אוויר נקי = literally air clean = clean air

This is the normal Hebrew word order for noun + adjective.

Because adjectives in Hebrew must agree with the noun in:

• gender
• number
• definiteness

Here, אוויר is masculine singular and indefinite, so the adjective is also masculine singular and indefinite:

• אוויר נקי = masculine singular
• אוויר נקייה would be wrong, because נקייה is feminine singular

If the noun were definite, the adjective would also become definite:

• האוויר הנקי = the clean air

Because the sentence means clean air, not the clean air.

In Hebrew, if the noun is definite and has ה־, the adjective must also be definite:

• אוויר נקי = clean air
• האוויר הנקי = the clean air

So the lack of ה־ shows that אוויר נקי is indefinite.

Yes, but usually when צריך is followed by an infinitive, not a noun.

In your sentence, צריך is followed by a thing that is needed:

• הכלב צריך אוויר נקי = The dog needs clean air

But with an action, Hebrew uses an infinitive, which usually has ל:

• הכלב צריך לנשום = The dog needs to breathe

So:

• צריך + noun → no ל
• צריך + infinitive → usually yes, because Hebrew infinitives normally begin with ל

Yes. This is the neutral, standard order:

subject + צריך + object

So:

• הכלב צריך אוויר נקי

is the most natural basic phrasing.

Hebrew can move words around for emphasis, but this sentence is the straightforward everyday order.

Only צריך changes to agree with the subject.

Examples:

• הכלבה צריכה אוויר נקי = The female dog needs clean air
• הכלבים צריכים אוויר נקי = The dogs need clean air
• הכלבות צריכות אוויר נקי = The female dogs need clean air

The phrase אוויר נקי stays the same here because air is still masculine singular.