In which direction does the head of the molecules of the plasma membrane face? toward the middle

away from water

toward the outside

toward the head of another molecule

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium

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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.