Oxygen has an atomic number of 8. the n = 1 energy level has two electrons, and the n = 2 energy level has six electrons. oxygen's valence is
+2
-2
+1
-1

Which mantle is under the crust the upper mantle or the lower mantle i think it's upper let me know if i'm right

The picture shows a fishing technique called trawling. how might trawling affect marine biodiversity

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.