Topic: Interchange of Parts of Speech,

Best Answer Explained in Below-:

In the context of the provided options, we are identifying which word represents a noun. A noun is a part of speech that names a person, place, thing, or idea.

Let's analyze each option:

A) **Sign**: This is a noun as it refers to an object or symbol that conveys information.
B) **Song**: This is also a noun, as it denotes a musical composition that typically consists of lyrics and melody. A song embodies the qualities of a noun perfectly because it represents a tangible concept that can be performed, heard, and appreciated as an art form.
C) **Feed**: This can function as both a noun and a verb, depending on the context. As a noun, it refers to food given to animals or the act of feeding.
D) **Tell**: This is primarily a verb, meaning to communicate information or narrate.

While options A, C, and D can have noun forms or meanings, the clearest and most straightforward noun in this specific set is B) song. It distinctly represents an object (a type of music) rather than an action or concept and is what makes it the most fitting choice for the question "Which one is noun?"