In what way would readings from a digital thermometer be preferable to those from a liquid-based thermometer?
readings from a digital thermometer are easier to use when performing calculations.
readings from a digital thermometer can be more readily combined with computer software.
readings from a digital thermometer are more accurate.
readings from a digital thermometer are less prone to fluctuation.

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.