Chemistry
posted by Anonymous .
Which element has no stable isotopes?
1. (subscript)27 Co
2. (subscript)51 Sb
3. (subscript)90 Th
4. (subscript)82 Pb
I believe it's either 2 or 3, but I can't decide which. I'm not sure how to go about answering this question, how can you tell which have stable isotopes and which don't?

Personally, I think this is a very poor question; however, here is a chart.
http://en.wikipedia.org/wiki/Isotope_table_(divided) 
The elements mentioned on the list have 0,1,2 and 4 stable isotopes, but NOT in order.
You only have to browse through articles on stable isotopes to find out which one you need. For example, Google "stable isotope", the Wiki article provides a complete list. 
The answer will also explain why we don't see compounds of that element in the chemistry lab. Unstable isotopes are radioactive!

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