What is the meaning of the idiom "set free"?

to liberate

The idiom "set free" means to liberate or release someone or something from captivity, restraint, or bondage. So the answer is (4) to liberate.

The other options are incorrect.

• (1) to run away means to leave a place or situation quickly and secretly.
• (2) to give some benefit means to provide something that is helpful or advantageous.
• (3) to give something free means to provide something without charge or payment.