February 25, 2021, 08:45:54 AM
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Topic: Correct answer  (Read 902 times)

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Offline peterpan1372

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Correct answer
« on: September 10, 2017, 08:40:38 PM »
Hello,

Can someone help me out?

I already know that the mass number must be 13, but do not know why 2 and 3 are right too...

thanks for any *delete me*

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