What is the characteristic of an open resistor?

An open resistor is characterized by its extremely high resistance, effectively acting as an open circuit. In this condition, the flow of electric current through the resistor is interrupted due to a break in the conductive pathway. When a resistor is open, it no longer allows current to pass through it, which results in a resistance that approaches infinity. This is why option C is the correct answer.

The other characteristics do not apply to an open resistor. Low resistance signifies a path with minimal opposition to current flow, which contradicts the definition of being open. Normal resistance would imply that the resistor is functioning within its rated parameters, which is not the case with an open resistor. As for variable resistance, that typically refers to a component that can adjust its resistance depending on conditions, such as a rheostat or potentiometer, which also doesn't describe an open resistor.