Conservation of energy means that

Conservation of energy, denoted by option [D], states that energy can neither be created nor destroyed; it can only change forms or be transferred from one object to another. This principle, based on the first law of thermodynamics, asserts that the total energy of an isolated system remains constant over time, regardless of any internal changes. While energy transformations occur within the system, the total energy content remains constant. This fundamental concept underpins many scientific principles and practical applications, from understanding the behavior of physical systems to engineering design and environmental studies. Conservation of energy provides a powerful framework for analyzing and predicting the behavior of complex systems, ensuring that energy is accounted for and properly managed in various contexts, from mechanical systems to chemical reactions to celestial phenomena.