Answer:
The process of photosynthesis in plants releases oxygen into the atmosphere. Respiration by plants and animals, as they use the energy stored in food, and the process of decomposition of dead organisms, releases carbon dioxide into the atmosphere. All three work together to maintain the carbon dioxide-oxygen cycle.
Use a magnet to separate the iron from the sand.
The two molecules will only react if they have enough energy. By heating the mixture, you are raising the energy levels of the molecules involved in the reaction. Increasing temperature also means the molecules are moving around faster and will therefore "bump" into each other more often.
