The statement "The sum of emf`s and potential differences around a closed loop equals zero" is known as Kirchhoff`s voltage law (KVL), which holds true in electrical circuits. KVL is a consequence of the conservation of energy.

Option 1 - Ohm`s law relates the voltage across a resistor to the current flowing through it. While Ohm`s law is an important principle in circuit analysis, it does not directly explain why the sum of emf`s and potential differences around a closed loop equals zero.

Option 2 - Conservation of charge states that charge cannot be created or destroyed, but it does not directly explain why the sum of emf`s and potential differences around a closed loop equals zero.

Option 3 - Conservation of momentum is a principle from mechanics that deals with the amount of motion in a system. It is not directly relevant to electrical circuits or the sum of emf`s and potential differences.

Option 4 - The correct answer is conservation of energy. For a closed loop in an electrical circuit, the sum of emf`s (electromotive forces) and potential differences must equal zero because energy is conserved. Any energy supplied by a source (emf) is consumed by the elements in the loop (potential differences), resulting in