This is a reduction half-reaction. Initially, gold exists as

, and after the reaction, it has been converted to elemental gold. To make this possible, three electrons must be added to <span>

. This fits within the definition of reduction reactions, where the reactant gains electrons in the reaction.</span>
The vertical columns are groups
The horizontal rows are periods
You can see a physical change always but not always a chemical
When we wish to convert a gas to liquid we have to either
a) decrease temperature
b) increase pressure
In case of fire extinguisher the CO2 is found to be in liquid state, this is as the CO2 is pressurized at high pressure which keeps CO2 in liquid state
the ideal pressure and temperature conditions when CO2 gas can be converted to CO2 gas
Pressure = 5 - 73 atm
Temperature = -57 to 31 degree Celsius