Please help me thanks so much?!?.:;)...I’ll mark you.:;)))

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

A5.000 g sample of niso4 h2o decomposed to give 2.755 g of anhydrous niso4. what is the formula of the hydrate? what is the full chemical name for the hydrate? what is the molar mass of the hydrate? niso4•_h2o what is the mass % of water in the hydrate?

Which factor is likely to impact the possible number of compounds ?