How to determine whether a mixture is homogeneous or heterogeneous?

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

According to the diagram; a) identify the anode of the cell and write the half-reaction that occurs there b) write the overall equation for the reaction that occurs as the cell operates c) calculate the value of the standard cell potential ,e cell. d)write the shorthand notation of the cell above e)indicate the flow of the electrons on the diagram

How have the greenhouse gasses increased from the year 2000 to 2018