Which word is a noun?

The correct answer is "Pen" because it is a tangible item that can be physically touched and used, fulfilling the criteria for a noun. Nouns are words that name people, places, things, or ideas, and "pen" specifically refers to a common object used for writing.

In contrast, "Running" is a gerund or present participle that describes an action rather than naming a specific object. "Quickly" is an adverb that modifies verbs, adjectives, or other adverbs, providing information about the manner in which an action is performed. "Above" serves as a preposition or an adverb, indicating location or position but does not represent a person, place, or thing itself.

Thus, among the options given, "Pen" stands out as the only word that fulfills the definition of a noun, making it the correct choice.