For a given reaction, which statement is true? a. The equilibrium constant is always the
same number, but the concentration of
reactants and products can vary at
equilibrium.
b. The equilibrium constant is always the
same number as long as the
temperature is held constant.
c. The equilibrium constant is always the
same number as long as the pressure is
held constant
d. The equilibrium constant is always the
same number as long as the
concentration of CO2​ is held constant

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.

14 days is the half-life of phosphorus-32

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.