The error in this sentence has to do with using both "one" and "you" as pronouns in a single sentence. Once you being using one of these pronouns in a sentence, you should stick with it and not switch to using the other one in mid-sentence. This sentence's latter half begins with "one" and uses the phrase "as if one has walked," but near the end, it switches to using "you" when it says "when you step in the door." To correct this sentence's error, "when you step in the door" should be changed to "when one steps in the door."

You can't switch between "one" and "you." The sentence begins with "one" and has to keep using it for the remainder of the statement.

This sentence cannot decide who it's addressing; it uses both "your" and "one's." These should be kept consistent. The corrected sentence reads, "Riding your bicycle to work can help reduce your carbon dioxide footprint."

This sentence uses the wrong pronoun case. “I” is only used as a subject, and “me” is used as an object. Here, as the object of the preposition “between,” “me” is needed. The corrected sentence reads, "What was once a friendly argument between my brother and me quickly became a full-scale brawl."

The pronoun "I" is only used as the subject of a sentence. "Me" is used as the object of a verb or (as in this case) a preposition. The corrected sentence reads, "The awkward tension between me and Sam was, as it turns out, completely one-sided."

The phrase "between you and I" is incorrect because "you" and "I" are acting as the objects of the prepositional phrase "between you and I," where the objective forms of these pronouns ("you" and "me") should be used instead.

This sentence has a problem with pronoun case in the prepositional phrase "to Sharon and I." "I" is the subjective case of the first-person pronoun, but as an object of the preposition "to," the objective case of the first-person pronoun, "me," should be used. The corrected sentence reads, "I never heard the official announcement, but I received the news when Mark sent an email to Sharon and me."

The word "whom" is incorrect because it refers to the brother, who is the subject of the sentence (it is the younger brother who does the crying here). Therefore, the correct word choice would be "who."

This sentence contains an error in its use of the pronoun "me."  The proper subjects of the sentence are "my boyfriend" and "I."  "Me" is an objective pronoun, not a subjective pronoun (e.g., "My boyfriend gave the puppy to me." is correct, but "Me went to the animal shelter" is not correct.)  

When someone is left behind, that person is the object of the action. "Me" is the first person pronoun that is used as an object, not "I." Therefore, the word "I" should be changed to the word "me" in the sentence.