- Von hier bis zum Bahnhof sind 10 Kilometer.
- Von hier bis zum Bahnhof sind es 10 Kilometer.
Are they both correct?
For the second sentence, why is it „es“ instead of „sie“? And what is the function of it?
- Von hier bis zum Bahnhof sind 10 Kilometer.
- Von hier bis zum Bahnhof sind es 10 Kilometer.
Are they both correct?
For the second sentence, why is it „es“ instead of „sie“? And what is the function of it?
Grammarians nowadays distinguish between 4 possible syntactic roles of "es" in the German language:
Hast du das Buch gelesen? Ja, Ich habe es gelesen.
Wenn du glücklich bist, bin ich es auch.
Referential "es" refers to previously mentioned contents and can never be omitted.
Notice that "es" can be used as a generic pronoun for characterization. Some varieties use "das" for this purpose.
Ich kannte seinen Bruder. Es war ein bedeutender Arzt.
An der Ecke standen ein Mädchen und ein Junge. Es waren seine Kinder.
Occasionally one may also find "es" in place of a genitive pronoun.
Es gab viele Treppen, aber die Aussicht war es wert.
Es geht, regnet, gibt, usw.
Wie halten Sie es damit?
Impersonal "es" functions as a formal subject, rarely also as a formal object, and can never be omitted.
Es ist empfehlenswert, dass du Fragen stellst.
Empfehlenswert ist es, Fragen zu stellen.
Correlative "es" is comparable to referential "es". The difference is that it is used to indicate an upcoming clause. It is dropped only when it is preceded by the clause it refers to.
Dass du Fragen stellst, ist empfehlenswert.
Fragen zu stellen(,) ist empfehlenswert.
The above statement applies primarily to correlative "es" functioning as a subject. Exceptions have to be made for "es" functioning as a genitive/accusative complement.
Ich werde nicht (es) müde, deine Fragen zu beantworten
Ich bedauere (es), dass du nicht gekommen bist.
Depending on verbs, the omission of objective "es" can be either obligatory, optional or disallowed.
Es sind viele Menschen da.
Es wird mir geholfen.
Expletive "es" has no particular functions other than occupying the beginning of a sentence. It must be dropped if the beginning of a sentence is occupied by other sentential constituents.
Viele Menschen sind da.
Mir wird geholfen.
Back to your question: "Von hier bis zum Bahnhof sind es 10 Kilometer" is presumably the preferred variation. The use of "es" in this case seems to be impersonal rather than expletive.
It's about expletive words.
An expletive word is a word that is there only for grammatical reasons. English has two of them:
it
It rains.
The word »it« does not refer to the producer of the rain nor to something else. It has no real meaning. It is there just to make the sentence grammatically complete.
there
There are dogs that have white fur.
The word »there« does not refer to a certain place. It also has no real meaning, and it also exists in this sentence only for grammatical reasons.
German also has an expletive word, but only one, and this word is »es«, and you can use it to translate both English examples:
Es regnet.
Es gibt Hunde, die weißes Fell haben.
The German phases »es gibt« and »es sind« express the existence of something, similar to »there is« in English.
So, the correct sentence is this:
Von hier bis zum Bahnhof sind es 10 Kilometer.
You can think of it as a shorter form to say this:
Von hier bis zum Bahnhof gibt es eine Entfernung von 10 Kilometern.
This has not exactly the same meaning, but it can help you to understand the expletive »es«, becasue now you can translate it into English using the English expletive »there«:
From here to the train station there is a distance of 10 kilometer.
The sentence
Von hier bis zum Bahnhof sind es 10 Kilometer.
is another reordering of writing:
Es sind 10 Kilometer von hier bis zum Bahnhof.
With "Es" being the subject and "sind" being the verb.
Von hier bis zum Bahnhof sind 10 Kilometer.
This sentence does not have a subject, which is just incorrect for German sentences.