Thank you for your help. I have posted one more time about the use of 'it.'

1. The station is 50 meters away.

2. The station is 50 meters.

3. It is 50 meters away.

4. It is 50 meters.

5. The distance is 50 meters away.

6. The distance is 50 meters.
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Which ones are grammatical? And when there is no previous sentence, what does 'it' refer to in #3 and #4?

All are correct except for 2. Without a previous sentence, the meaning of "it" isn't clear in 3 and 4.

Let's analyze each sentence to determine which ones are grammatically correct and understand the use of "it" in sentences #3 and #4:

1. The station is 50 meters away. (Grammatical)
In this sentence, "the station" is the subject, "is" is the verb, and "50 meters away" is a prepositional phrase modifying the subject.

2. The station is 50 meters. (Grammatical but incomplete)
This sentence is missing additional information. While grammatically correct, it lacks clarity as it does not specify a direction or destination.

3. It is 50 meters away. (Grammatical)
In this sentence, "it" is used as a pronoun that refers back to something mentioned previously. Without a prior sentence to clarify the antecedent (the noun or phrase to which the pronoun refers), it may seem ambiguous. It is essential to establish context to fully understand what "it" refers to.

4. It is 50 meters. (Grammatical but incomplete)
Similar to sentence #3, "it" acts as a pronoun without a clear antecedent. In the absence of context, it is not precise or informative.

5. The distance is 50 meters away. (Grammatical)
This sentence uses "the distance" as the subject, "is" as the verb, and "50 meters away" as a prepositional phrase modifying the subject.

6. The distance is 50 meters. (Grammatical)
This sentence uses "the distance" as the subject, "is" as the verb, and "50 meters" as a noun phrase complementing the subject.

To summarize, sentences #1, #3, #5, and #6 are grammatically correct. Sentences #2 and #4 are grammatically correct but may lack clarity without additional information. When #3 and #4 are used with no previous sentence, the referent for "it" is not explicitly stated, so they might sound vague or incomplete without contextual information.