When sodium, magnesium and copper are left in the air, sodium reacts strongly with oxygen to form sodium oxide, magnesium reacts with oxygen to form magnesium sodium oxide only when heated, and copper does not burn in air, even when heating the wire. . It reacts only with prolonged heating. This shows that sodium is the most reactive and then magnesium and copper are the least reactive of the three.
Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen, magnesium does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen but copper does not react even with steam. This shows that sodium is very reactive, magnesium is less reactive than sodium, and copper is the least reactive of the three.
Final answer:
Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen, magnesium does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen but copper does not react even with steam. This shows that sodium is very reactive, magnesium is less reactive than sodium, and copper is the least reactive of the three.