All atoms of the same element have the same: question 13 options: mass number. mass. number of protons. number of neutrons.

Number of protons

Explanation:

The number of protons (the atomic number) determines the identity of the element.

The number of neutrons may differ, in which case the mass and the mass number (number of protons + neutrons) will differ, but all atoms of the same element will have the same number of protons.

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

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.