Why are nobel gases grouped together on the periodic table?

Nobel gases also referred as inert gases, they are grouped together because they are the most stable elements. This explains why they are nonreactive. They do not form chemical bonds because they only have a little tendency to either gain or lose an electron, since they have 8 electrons in the outer shell (except for helium as it has 2 electrons in the outer shell). As a result, they do not react with any other element in the periodic table.

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.

i think   the answer is c hope i'm right