Here's why:
* Subject-Verb Agreement: A sentence needs a subject (who or what is doing the action) and a verb (the action). "Broken" is an adjective describing a state of being, not an action.
* Pronoun Usage: Pronouns replace nouns. To use a pronoun like "it," you need a noun to refer to: "My pencil is broken."
Here are some examples of how you could use a pronoun for "my pencil" in a complete sentence:
* "My pencil is broken, so I can't write." (Here, "it" replaces "my pencil")
* "I broke my pencil, and now it's useless." (Again, "it" replaces "my pencil")