Question

highlight the noun that is the simple subject.
noun/pronoun verb article adjective preposition adverb conjunction
the students are ready to leave now.

Explanation:

The simple subject is the main noun that the sentence is about, stripped of any modifiers. In "The students are ready to leave now," "The" is an article modifying the noun, and "students" is the core noun performing/being the focus of the verb "are".

Answer:

students