1s2, 2s2, 2p6, 3s2, 3p6, 4s2
How many shells does this atom have?

4

Explanation:

4 periods

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.

la respuesta es si te gusta hacer lo que siempre haces cuando nunca ves a alguien en el espejo porque sabes que no siempre están ahí.