The correct answer is the law of conservation of energy.

• The law of conservation of energy is also referred to as the first law of thermodynamics.
• The first law of thermodynamics states that the energy of the universe is constant.
• However, while it can be exchanged between the system and the surroundings, it cannot be created or destroyed.
• The law essentially relates to changes in energy fields due to work and heat transfer.
• The total energy of a system remains conserved.
• The equation for the first law of thermodynamics is as follows:
  • ΔU = q + W
  • Where,
  • ΔU = change in internal energy of the system
  • q = algebraic sum of heat transfer between the system and the surroundings
  • W = work done by the system interacting with its surroundings