Option 1 -> Flexible means easily adaptable or pliable, which is the opposite of obdurate.
Option 2 -> Gentle means kind and mild-mannered, contradicting the hardened nature of obdurate.
Option 3 -> Stubborn means refusing to change one's mind or course of action, which directly matches the meaning of obdurate.
Option 4 -> Weak implies lack of strength, whereas obdurate suggests unyielding firmness.
Hence, Option 3: Stubborn -> Obdurate describes someone who is stubbornly persistent in wrongdoing or refusing to change their attitude, making "stubborn" the closest synonym -> correct