The correct answer is B. Decrease.
When a bond is formed between two atoms, the energy of the system will decrease. This is because the atoms will be more stable when they are bonded together than when they are separate. The energy released when the atoms bond is called the bond energy.
Option A is incorrect because the energy of the system will decrease when a bond is formed.
Option C is incorrect because the energy of the system will decrease when a bond is formed.
Option D is incorrect because the energy of the system will always decrease when a bond is formed.