Does atomic increase or decrease as you go down a group/family on the periodic table

How many atoms are there in 5.70 mol of mg

How many moles is 14.5 cm^3 of platinum? the density of platinum is 21.45 g/cm^3.

Aroom with dimensions 7.00m×8.00m×2.50m is to be filled with pure oxygen at 22.0∘c and 1.00 atm. the molar mass of oxygen is 32.0 g/mol. how many moles noxygen of oxygen are required to fill the room? what is the mass moxygen of this oxygen?