Which human activity contributes to air pollution

Answerthe valence of an element or radical is equal to the number of positive or negative charges on the ion.

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.