40,500 mg---> 3 SF Zeros to the left of an understood decimal point and at tge same time to the right of a non zero number and not significant. The zero in between non zeros(4&5) is significant.
Solids hold their shape and have a fixed volume. The molecules in solids are packed closely together and could not be moved. Solids also have a slow diffusion and low vapor pressure. Hope that helped!
The answer is B.mass because like the periodic table it determines the elements by mass