Lead glass contains 18-40% by mass of pbo (instead of cao in regular glass). lead glass is still used industrially, but lead crystal drinking goblets are no longer considered safe, as the lead may leach out and cause toxic responses in humans. a particular 286-g lead crystal goblet that holds 550 ml of liquid is 19 % pbo by mass, and it leaches 4.2 micrograms of lead every time it is filled.

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.