Which of the following environment events is observed by switching off all lights at homes, business establishments, landmarks and so on for an hour?

Earth Hour

The correct answer is Option (2) - Earth Hour

The environment event observed by switching off all lights at homes, business establishments, landmarks, and so on for an hour is  Earth Hour.

Earth Hour is a global event held annually on the last Saturday of March where people are encouraged to switch off their non-essential lights for an hour to raise awareness about climate change and energy conservation.