According to Plato, which class should govern the ideal state?

Correct option is A

The correct answer is a) Philosopher-kings.

Plato's vision of the ideal state, known as Kallipolis, is presented in his masterpiece, The Republic. He argues that a society can only be truly just when it is ruled by individuals who possess true wisdom and are guided by reason.

The Philosopher-King
Plato famously stated: "Until philosophers are kings, or the kings and princes of this world have the spirit and power of philosophy... cities will never have rest from their evils."

A Philosopher-king is someone who has:

Knowledge of the Forms: Unlike ordinary citizens who perceive only shadows of reality, the philosopher has "seen" the eternal and unchanging Form of the Good.
Intellectual Rigor: They undergo a decades-long education process, studying mathematics, music, and dialectic (philosophy).
Moral Integrity: Because they love truth above all else, they are deemed incorruptible and have no desire for the material rewards of power.