Which of the following has the most stable nucleus? fe he u b

Fe

Explanation:

Ferrum [Iron] has the most stable nucleus because of binding energy per nucleon. Although Uranium is another possibility, in this case, it is more radioactive than Iron. It disintegrates very swiftly that all is done so, just to achieve stability.

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c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.