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What physical changes happen when plutonium is exposed to air?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transuranium element Modern version of the periodic table of the elements (printable).

When plutonium is exposed to air, the silvery metal undergoes a physical change by taking on a yellow tarnish.1