The first law of thermodynamics protects

The first law of thermodynamics, or the law of energy conservation, is fundamental in physics and thermodynamics. It asserts that the total energy in an isolated system remains constant. This means energy can neither be created nor destroyed; it can only change forms, such as from kinetic to potential energy, or from chemical energy to thermal energy. The principle does not directly address momentum, which is conserved in a different context under Newton’s laws of motion. The conservation of energy applies universally across all processes, ensuring that the total energy before and after any transformation or transfer remains equal. This law underpins much of modern physics and engineering, dictating how energy systems are analyzed and designed. Thus, while momentum conservation is a crucial concept in its own right, it is the conservation of energy that is explicitly protected by the first law of thermodynamics. Therefore, the correct answer is [B] Energy.