10.0 g of Mg(NO3)2 = moles

Which is the layer underground where all empty spaces are filled with a combination of air and water ?

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?

What overall charge must all compounds have