La loĝantaro de la urbo kreskas.

Because the sentence contains two separate definite nouns:

• la loĝantaro = the population
• la urbo = the city

In Esperanto, each noun gets its own la if it is definite. So de la urbo means of the city, not just of city.

Loĝantaro is made from smaller parts:

• loĝ- = live, reside
• -ant- = someone doing the action
• -ar- / -aro = a collection or group
• -o = noun ending

So loĝanto means inhabitant / resident, and loĝantaro means the body of inhabitants, that is, the population.

This is different from just loĝantoj, which means inhabitants as individual people.
So:

• loĝantoj = inhabitants
• loĝantaro = population as a group

De often means of or from, and here it shows a relationship like English of:

• la loĝantaro de la urbo = the population of the city

English sometimes uses an apostrophe or noun-noun structure, like the city's population, but Esperanto normally uses de for this kind of idea.

Yes. La urba loĝantaro kreskas is also natural.

Here, urba is the adjective form of urbo, meaning urban or city-related. So:

• la loĝantaro de la urbo = the population of the city
• la urba loĝantaro = the city population / urban population

The version with de la urbo is a very direct match for English of the city. The version with urba is a little more compact.

The ending -as marks the present tense in Esperanto.

So:

• kreski = to grow, increase
• kreskas = grows / is growing / increases / is increasing

Esperanto does not change the verb for different subjects:

• mi kreskas
• vi kreskas
• la loĝantaro kreskas

The verb form stays kreskas in the present tense.

It can mean either, depending on context.

Esperanto -as covers the general present tense, so kreskas can correspond to English:

• grows
• is growing
• increases
• is increasing

In this sentence, English would often translate it as is growing or is increasing, but Esperanto does not force that distinction.

Because there is no direct object here.

The sentence has:

• subject: La loĝantaro de la urbo
• verb: kreskas

Kreski is not taking an object here; it just describes what the subject is doing. The population is growing.

So there is no reason to add -n.

Urbo is often translated as city or town, depending on context. Esperanto does not always draw the same sharp line that English sometimes does.

So la urbo could mean:

• the city
• the town

If the meaning has already been given to the learner as city, then that is the intended sense here.

A helpful approximate pronunciation is:

• lo-ĵan-TA-ro

More exactly:

• ĝ sounds like the s in measure or the g in genre
• the stress in Esperanto is always on the second-to-last syllable, so loĝanTAro
• every written vowel is pronounced clearly

So loĝantaro has four syllables: lo-ĝan-ta-ro.

Not completely. Esperanto word order is fairly flexible, though the normal order is subject + verb:

• La loĝantaro de la urbo kreskas.

That is the most neutral version.

You could change the order for style or emphasis, but learners should generally keep the normal pattern unless they have a reason not to.

Because kreski already means to grow / to increase. It is a complete verb by itself.

So Esperanto can simply say:

• La loĝantaro kreskas.

There is no need for an extra verb like is plus another word. This is very common in Esperanto: one clear verb often does the job that English expresses with a longer phrase.

Not with exactly the same meaning.

• La loĝantoj de la urbo kreskas would literally mean the inhabitants of the city are growing
• that could sound like the people themselves are growing in size, or it might be understood awkwardly as the number of inhabitants is increasing

If you mean population as a whole, loĝantaro is much better and more precise.

Yes, it is natural and straightforward Esperanto.

It uses very standard patterns:

• la for definite nouns
• de for of
• a noun with -aro to show a group or collection
• -as for present tense

So for a learner, this is a very good example of clear, normal Esperanto structure.