1. a vertical column of elements in the periodic table 2. 1/12 the mass of a carbon-12 atom 3. a horizontal row of the periodic table 4. dalton's atomic theory included the idea that the atoms of different elements can chemically combine in ratios

According to the article, what valid claim came from the national research council? there is no association between fluoride exposure and increased cancer risk in humans. there is a possible link between fluoride exposure and increased cancer risk in humans. there is a definite link between fluoride exposure and increased cancer risk in humans.