calculate the mass in milligrams of:
1) 10^21 atoms of U-238
2) 10^20 molecules of SO2 gas

I know the step to solve this I.e.
1) n=N/avagadro no.
m= nM = N/avgadro no. M
= (10^21 / 6.022 10^23) 238g
but I am not able to simplify this :( plzz help!! in the nxt part of the ques I am stucking when it comes to simplification...
2) ,....... (10^20 /6.02210^23) 64g

Dear student
 Given number of atoms = 1021 atoms
Molar mass of U-238 = 238 g mol-1 
Number of moles (n)= Given mass (m) Molar mass (M) n = Given number of particles (N)Avagadro number (NA)m = NNA×Mm = 10216.022×1023×238 = 39.521×10-2 g 1 g = 1000 mg Hence , mass will be 39.521×10-2×103 = 39.521×10 mg You should divide 238 by 6.022 . 

Regards

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