The correct answer is: C. Does not support combustion.
Nitrogen is used in electric bulbs because it does not support combustion. This means that it will not react with the filament in the bulb, which is what produces the light. If a different gas were used, it could react with the filament and cause it to burn out more quickly.
Option A is incorrect because nitrogen is not lighter than air. In fact, it is slightly heavier than air.
Option B is incorrect because nitrogen does not produce more light in the bulb. The amount of light produced by a bulb is determined by the power of the bulb and the type of filament used.
Option D is incorrect because nitrogen is not toxic. It is a safe gas to use in electric bulbs.