Option 1 -> Petrify means to paralyze with fear or turn to stone, not related to energy levels.
Option 2 -> Vitalise means to give strength, energy, and vitality - directly opposite to weakening.
Option 3 -> Gratify means to please or satisfy, unrelated to strength or energy.
Option 4 -> Debilitate means to weaken or drain strength - this is actually a synonym of enervate, not an antonym.
Hence, Option 2: Vitalise -> Enervate means to weaken or drain of energy, while vitalise means to energize and give life or strength to something, making them perfect antonyms. -> correct