The identity of an element is defined by its number of for example, every atom of carbon has protons and only atoms with 6 protons are however, atoms of the same element can have number of neutrons. when atoms of the same element have different numbers of neutrons they are called . since the mass of an atom is determined by the total number of protons and neutrons, isotopes of the same element will have different despite having the numbers of protons. also, isotopes of the same element will have similar behavior. this is because chemical is based on the number of and isotopes only have different numbers of

Astudent made a graph plotting the progress of a reaction over time. the student forgot to label the y-axis of the graph. a graph is shown with two graph lines. one graph line starts at a higher position on the y axis and slopes downwards towards the right. the other graph line starts at a lower position on the y axis and slopes upwards towards the right. the two graph lines stop short of intersecting each other and continue as separate lines which gradually become straight and parallel to the x axis. a vertical line is shown at a point where the two graph lines finally became parallel to the x axis. this vertical line is labeled equilibrium. the title on the x axis is time and an arrow pointing towards the right is shown above time. the title on the y axis is left blank. what best explains the label that the student should use on the y-axis? amount, because as the amount of product decreases, the amount of reactant increases over time. reaction rate, because forward and backward reaction become equal at equilibrium. amount, because the amounts of reactants and products become constant after equilibrium is reached. reaction rate, as the rate of forward reaction increases and rate of backward reaction decreases over time.