The existence of isotopes violates one of the original ideas of dalton's atomic theory. which one? matter is composed of exceedingly small particles called atoms. an atom is the smallest unit of an element that can participate in a chemical change. an element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element. atoms of one element differ in properties from atoms of all other elements. a compound consists of atoms of two or more elements combined in a small, whole-number ratio. in a given compound, the numbers of atoms of each of its elements are always present in the same ratio. atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change.

specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.