Explanation:

The first law of thermodynamics, also known as the law of energy conservation, states that energy cannot be created or destroyed in an isolated system. It can only be transferred or converted from one form to another. This law is a consequence of the conservation of energy.

Conservation of Energy:
- Energy is a fundamental quantity in physics that can exist in various forms such as mechanical, thermal, electrical, chemical, etc.
- The total energy of a closed system remains constant, regardless of the transformations it undergoes.
- This principle is known as the conservation of energy and is a fundamental principle in physics.

First Law of Thermodynamics:
- The first law of thermodynamics is a specific application of the conservation of energy principle to thermodynamic systems.
- It states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.
- Mathematically, it can be expressed as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
- This equation shows that energy can be transferred between a system and its surroundings in the form of heat or work.

Consequence of Conservation of Energy:
- The first law of thermodynamics is a consequence of the conservation of energy because it states that the change in internal energy of a system is equal to the energy added to or subtracted from the system.
- When heat is added to a system, it increases the internal energy of the system, resulting in an increase in temperature or phase change.
- Similarly, when work is done by a system, it decreases the internal energy of the system.
- The first law of thermodynamics ensures that the total energy of a system remains constant, even though it may change its form.

Conclusion:
- The correct answer to the question is option 'B' (energy) because the first law of thermodynamics is a consequence of the conservation of energy.
- This law states that energy cannot be created or destroyed, only transferred or converted from one form to another.
- The first law of thermodynamics mathematically expresses this conservation of energy principle in terms of the change in internal energy, heat, and work.