Acidified sodium potassium tartrate solution was mixed with hydrogen peroxide solution
in a boiling tube.
When pink cobalt(II) chloride solution was added to the mixture, there was rapid
effervescence as carbon dioxide was produced and the solution turned green
After a few seconds, the effervescence stopped and the solution turned back to pink.
From these observations it can be deduced that the cobalt(II) ions are acting as
A a catalyst.
B a dehydrating agent.
C an oxidizing agent.
D a reducing agent.