Final answer:
The correct answer is d) Reactive change, which occurs spontaneously in an imbalanced system without the need for a continuous input of energy. Reactive changes are emergency responses, whereas spontaneous changes abide by the principle of increasing disorder or entropy in the universe.
Step-by-step explanation:
The type of change that occurs without prior planning and is a result of an imbalance in the system is d) Reactive change. This is in contrast to a spontaneous change, which is a process that takes place without a continuous input of energy from an external source. Reactive changes are often immediate responses to unexpected issues and can occur rapidly, necessitating a sudden release of energy or resources.
It's important to note that spontaneous changes are those that tend to move a system to a more stable state by releasing free energy. In general, systems in the universe are naturally inclined to become disordered spontaneously, leading to an increase in entropy. The concept of spontaneity helps us to understand how the distribution of energy and matter within a system is affected without needing an ongoing input of energy.