Posted by **Sanjay** on Saturday, March 3, 2007 at 8:50pm.

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years?

A. 2.0 grams of 198 Au

B. 2.0 grams of 42 K

C. 4.0 grams of 32 P

D. 4.0 grams of 60 Co

By the way the numbers next to the elements are their atomic masses. thanks again

You must look up the half-life of each of the isotopes. Surely you have a text or notes that will furnish this. Co-60 is the only one I know from memory for I worked with it many years ago. It is 5.1 years half-life. Then half of the mass will remain after 1 half life, 1/4 will remain after two half lives, etc.

You can also use

ln(No/N)=kt I can help with that if you need help after you obtain the half lives.

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