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1). A radioactive compound cobalt-60 has a half-life of 527.0 years. What will be the amount remaining in a 100.0-g sample after 15.816.0 years?
2).An 80.0-g sample of a radioactive compound,radium-266, is reduced to 5g in 28 years. What is the half-life of the compound?
3).How many significant digits are there in 6.023x10^23 molecules?
4). Write the shorthand form of the electron configuration for sodium.
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I don't like working with formulas, but here is a link to help you with 1 & 2
http://en.wikipedia.org/wiki/Half-life
the next two are pretty simple: 3. 4 4. Na: [N e] 3s1
correction on #4...
Na: [any] 3s1