Which statement is the best definition of an atom? a) anything that has mass and occupies space. b) the smallest particle that has the properties of an element. c) a substance that cannot be broken down chemically into simpler substances. d) the smallest unit of a substance that exhibits all of the properties characteristic of that substance.

c)  A substance that cannot be broken down chemically into simpler substances.

Explanation:

The smallest particle that has the properties of an element, is the correct definition of an atom. A is the definition of matter; C is the definition of an element; and D is the definition of a molecule.

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.