Which is more concentrated 200 ML of an 8-M NaOH solution or 500 mL of a 4-M NaOH solution

200 ML of an 8-M NaOH solution; The higher the molarity, the higher the concentration of the substance. The volume of the 8M NaOH solution is less as well.

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.

thats a little if u want the answer just look it up on google thats what i do haha : )