A sample of argon has a volume of 1.2 L at STP. If the temperature is
increased to 22°C and the pressure is lowered to 0.80 atm, what will
the new volume be, in L?

the new volume would be 1.62 L

Explanation:

stp is 0 degrees C or 273.15 K and 1atm for the pressure

22 degrees C is 295.15 K

use the combined gas law formula and solve for v2

v2=p1(v1)(t2)/p2(t1)

v2=1atm(1.2L)(295.15)/0.8atm(273.15K)

v2=1.62

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.