What is the smallest unit on the celsius thermometer?

The thermometer is used to measure the temperature. There are several scales to determine the temperature, which are Celsius, Fahrenheit and kelvin. The range of measurement scales are different for each of the scales or unit of temperature. For Celsius scale earlier the lowest temperature was 0°C, but after the invention of absolute zero which is 0 K (K = Kelvin). The lowest temperature of Celsius scale is -273°C. Thus the smallest unit of Celsius scale is -273°C.      

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.