How do you know if the resistor is defective?

To determine if a resistor is defective, you can measure its resistance using a multimeter. If the measured resistance significantly deviates from the resistor's specified value (indicated by its color code), it may be faulty. Additionally, visual inspection for physical damage, such as burns or cracks, can also indicate a defective resistor. If the resistor is part of a circuit and the circuit is not functioning properly, it may be worth testing the resistor as a potential cause.