The sum of the currents into a junction equals the sum of the currents out of the junction is a consequence of:

The answer is a) conservation of charge.

This principle, often referred to as Kirchhoff’s Current Law, is based on the conservation of charge, which states that charge cannot be created or destroyed in a closed system. At any junction in an electrical circuit, the electric charge flowing into the junction must equal the amount of charge flowing out. This ensures that the total charge is conserved throughout the circuit. Understanding this concept is crucial for analyzing electrical circuits effectively.