According to its periodic table entry, how many electrons does kr have in its valence level?
2
8
18
7

Several kinds of bears are found on earth. most bears are brown or black, but one type of bear, the polar bear, is white. what process led to this difference in fur color? explain your answer.

Mary is conducting an experiment on how pollution affects plant growth. how can she ensure that her data are reliable?

What produces wave a)sound b) heats c)transfer of energy d)vibrations