. The shell around the nucleus can be numbered from near to the nucleus as 1, 2, 3, 4, 5 or represented by the letters, K, L, M, N, O,​

He numbered these orbits due to their location.

Explanation:

Scientist Neil Bohr in his atomic model describes that electrons are moving with high velocity in circular paths around the nucleus is called shells or orbits. As long as electrons are in their particular orbit their energy is constant. He named those orbits as K- shell, L- shell and M- shell etc. When the electron absorb energy, it is able to jump to the next shell and comes back to its original shell when it loses energy. He also give numbers i.e. 1,2,3,4 to the shells due to their nearness to the nucleus. Shell 1 is near to the nucleus whereas shell 4 is farther from the nucleus.

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.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation: