What does reactivity with water mean?

Answer 1

Does the material react chemically with plain water and how violently it reacts:

• sand, sugar, glass, chlorine gas, motor oil, gold, and TNT are not reactive with water.
• iron is just barely reactive with water, slowly rusting over a period of years (for practical purposes this is considered as not reactive).
• magnesium is very slightly reactive with water, it slowly produces hydrogen and magnesium hydroxide.
• baking powder mixture is mildly reactive with water at room temperature, giving off carbon dioxide gas harmlessly.
• calcium is fairly reactive with water, producing a white calcium oxide and calcium hydroxide and hydrogen.
• calcium carbide is significantly reactive with water, giving off acetylene gas which can be ignited.
• aluminum phosphide is significantly reactive with water, giving off highly toxic phosphine gas.
• lithium, sodium, and potassium are violently reactive with water, giving off hydrogen gas and often spontaneously igniting the gas. The metal may melt and spray out molten droplets! The water becomes dangerously alkaline with dissolved lithium hydroxide, sodium hydroxide, or potassium hydroxide respectively and the water may boil!
• etc.