Understanding the elements

• Why does water produce an explosion with sodium but not with iron? Experiment: Sodium soup​
• Why do you need paraffin oil to store lithium but not magnesium?
• Why are fluorine in toothpaste and chlorine in table salt both toxic yellow gases in their pure forms?
• Why is mercury, found in old-fashioned thermometers, also called quicksilver? Hg, mercury, quicksilver (elohopea)​