What is included in earths hydrosphere?

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?

‘which reaction would most likely require the use of an inert electrode?

Which sample at stp has the same number of atoms as 18 liters of ne at stp