The correct answer is option 2, which is 16 degrees Celsius. The mean temperature of Earth refers to the average temperature across the entire planet. It takes into account the temperatures at different locations and at different times of the year. 16 degrees Celsius is an approximate value and can vary slightly depending on the source and the period of time being considered. It`s important to note that this value represents the average temperature of the Earth`s surface, including both land and ocean. The average temperature of the entire Earth, including the lower atmosphere and the core, would be significantly different.