The correct answer is: White.
An IBS (Incandescent Bulb with Screw Base) shows white light in normal condition. It is a type of light bulb that uses a filament to produce light. The filament is made of a material that has a high resistance to electricity, such as tungsten. When electricity flows through the filament, it heats up and emits light. The color of the light emitted by an IBS depends on the temperature of the filament. The hotter the filament, the bluer the light will be. The cooler the filament, the redder the light will be. In normal condition, the filament of an IBS is heated to a temperature of about 2,500 degrees Fahrenheit. This produces a white light.
The other options are incorrect because they are not the colors of light that are emitted by an IBS in normal condition. Red, green, and yellow are all colors of light that are emitted by other types of light bulbs, such as fluorescent bulbs and LED bulbs.