What are the three major biomes found in the United States? taiga, tundra, deciduous forest
deciduous forest, taiga, tropical rainforest
deciduous forest, grassland, desert
grassland, desert, taiga

The answer is the first option just took the test

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.