Q. Which of the metals have the greatest affinity to oxygen?
A. Those called potassium and sodium.
Potassium and sodium derive their names from potash and soda. Potassa is the oxide of potassium; and soda is the oxide of sodium.
Q. How is the affinity of potassium and sodium for oxygen shewn?
A. They decompose water the moment they are brought into contact with it.
Q. What effect has potassium on water?
A. It catches fire the moment it is thrown into water, and burns with a vivid flame, which is still further increased by the combustion of hydrogen separated from the water.
(N.B. Water is composed of oxygen and hydrogen; and potassium separates the two gases.)
Q. What effect has sodium on water?
A. It does not take fire as potassium does, but undergoes very rapid oxidation.