How is the trend of atomic number evidenced in the structure of the atoms of each element

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?

Calculate the number of molecules present in 0.750 mol of mgo.

When hydrochloric acid reacts with potassium hydroxide solution, the following reaction occurs. hcl (aq) + koh (aq) h2o (l) + kcl (aq) the reaction gives off heat energy, so it is an reaction.