Final answer:
The independent variable in the scenario where the effect of light exposure on the number of eggs laid by chickens is investigated is the duration of light exposure.
Step-by-step explanation:
In the given scenario where an investigation was conducted to see if keeping the lights on for different amounts of time each day affected the number of eggs chickens laid, the independent variable is B. The duration of light exposure. The independent variable is the factor that is changed or controlled in an experiment to test the effects on the dependent variable. In this case, the duration of light that the chickens are exposed to is manipulated to observe the effect on the number of eggs they lay, which is the dependent variable.