When studying the movement of heat, what does the term "system" refer to? what does "surroundings" refer to?

Plz choose one of the compounds from the table and explain how you know the numbers of atoms in your formula. is it possible for two different compounds to be made from the exact same two elements? why or why not? with a limited number of elements (less than 120 are known), does this mean we also have a small number of compounds or do we have a large number of compounds in this world?

If 1.8 l of water is added to 2.5l of a 7.0 molarity koh solution, what is the molarity of the new solution

Which substance is a steroid? cholesterol fatty acid monosaccharide trans fat