Which have different numbers of electrons? different ions of an element
different isotopes of an element
the nucleus of an element
each of the atoms of an element

different ions of an element

Explanation:

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

it's c. elements are placed in rows based on how may valencies electrons have.