What occurs when zero visibility is caused by heavy snowfall combined strong updrafts and downdrafts

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Which of the following statements is true? a. elements in the last period are radioactive. b. atomic weight is the same as atomic mass. c. elements in the same group have the same number of electron shells. d. atomic number equals the number of neutrons in the nucleus of an atom.

How can parts of a solution be separated by chromatography?