Which sentence contains the correct form of the possessive pronoun?

None, apparently.

To determine which sentence contains the correct form of the possessive pronoun, we need to understand what a possessive pronoun is. A possessive pronoun is a word that shows ownership or possession. Examples of possessive pronouns include "mine," "yours," "his," "hers," "ours," and "theirs."

Let's analyze the given sentences to identify the correct form:

1. "The book is her's."
2. "That pen is your's."
3. "This car is ours."
4. "Their house is beautiful."

In the first sentence, we see the word "her's." However, the correct form of the possessive pronoun "hers" does not require an apostrophe. Therefore, sentence 1 is incorrect.

In the second sentence, it includes the word "your's." Similarly, the correct form of the possessive pronoun "yours" does not need an apostrophe. Therefore, sentence 2 is also incorrect.

In the third sentence, we find the phrase "is ours." Here, the possessive pronoun "ours" does not need an apostrophe and is correctly used. Therefore, sentence 3 is correct.

In the fourth sentence, we see the word "Their" used before the noun "house." This is the correct form of the possessive pronoun "theirs." Therefore, sentence 4 is correct.

To answer the question, the sentence that contains the correct form of the possessive pronoun is Sentence 3: "This car is ours."