There is a tremendous weight pushing down on the center of the Earth because of so much population stomping around up there these days. Many dead animals in the past changed to fossils while others preferred to be oil. Vacuums are nothings. We only mention them to let them know we know they're there. Some oxygen molecules help fires burn while others help make water, so sometimes it's brother against brother.
Some people can tell what time it is by looking at the sun.
But I have never been able to make out the numbers. To most people solutions mean finding the answers. But to chemists solutions are things that are still all mixed up. Clouds are high-flying fogs. I am not sure how clouds get formed.