Which two changes of state can occur when a substance gains thermal energy? A. Vaporization
B. Condensation
C. Deposition
D. Sublimation

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

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Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.