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a) The mass of the isotope 25/11Na is 24.99u. How many atoms are in a sample...

a) The mass of the isotope 25/11Na is 24.99u. How many atoms are in a sample of 25/11 Na whose mass is 0.5g?

b) What is the activity of a 0.50g of sodium isotope 25/11 Na at time=1000s if its activity at t = 0 is 1.392x10^20s^-1? You can use the number of atoms obtained from the above problem directly.

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