The element sodium (na) is a soft solid that will react explosively with water. the element chlorine (cl) is a toxic gas. when these two elements combine, they produce a stable, crystalline solid known commonly as table salt (nacl). how would you explain this?
select one:

when substances combine to form new substances, the properties of the reactants are preserved.

when substances combine to form new substances, the properties of the resulting substances will be different than those of the reactants.

sodium and chlorine become different elements during the reaction.

the properties of each of the two original elements are combined to give salt its properties.

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.

In the particles are arranged in a regular, repeating pattern. a)a crystalline liquid b)a crystalline solid c)all gases d)all solids

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.