The correct answer is C. 1.
A switch is a simple on/off device. When a switch is turned on, it completes an electrical circuit and allows current to flow. When a switch is turned off, it breaks the circuit and prevents current from flowing.
In a computer, switches are used to represent binary numbers. A binary number is a number that is represented using only two digits: 0 and 1. The number 1 is represented by the ON state of a switch, and the number 0 is represented by the OFF state of a switch.
Therefore, the ON state of a switch is represented by the number 1.