The statement (a) say that the switch is the source of electric current in the electric circuit but we know that the source of electricity in an electric circuit is an electric cell. An electric cell provides current in the source, while switch only helps to complete or break the circuit.

According to Statement (b), the switch helps to complete or break the circuit which is true because it breaks the circuit when it is on "OFF" mode but it completes the circuit when it is on "ON" mode.

Statement (c): When we "OFF" the switch the circuit breaks and the bulb goes off but when we "ON" the switch the circuit completes and the bulb glows, hence the switch help us to use the electricity as per our requirement. So statement (c) is true.

Statement (d) says that when the switch is open or "OFF" the circuit breaks and the bulb goes off. Which happen because there is an air gap between its terminal and hence the statement (d) is also true.