Due to the high reactivity of sodium, it is usually stored under

Step 1: Analyze the question Sodium is a highly reactive alkali metal. The question asks which substance it is stored under to keep it safe and unreacted.

Step 2: The concept Sodium reacts readily with:

• Oxygen in air, forming sodium oxide and tarnishing quickly
• Water and moisture, reacting violently: 2Na + 2H₂O → 2NaOH + H₂↑ (exothermic, and the hydrogen can ignite)

So it must be stored in a liquid that is inert and does not contain oxygen or water, and in which sodium is insoluble and less dense (sodium is denser than paraffin and sinks, so it stays covered).

Step 3: Evaluate the options

• A. Water: Wrong. Sodium reacts violently with water.
• B. Mercury: Wrong. Sodium dissolves in mercury to form an amalgam, so this is not storage. It is also toxic and impractical.
• C. Paraffin: Correct. Paraffin (kerosene) is a hydrocarbon, unreactive towards sodium, and it keeps out air and moisture.
• D. Phenol: Wrong. Phenol is acidic and has an -OH group, so it reacts with sodium to form sodium phenoxide and hydrogen gas.

Step 4: Answer Sodium is stored under paraffin (kerosene), which is option C.

Exam tip: Remember "Li, Na, K are kept in oil." Lithium is so light that it floats on oil, so it is often wrapped in paraffin wax. Whenever you see a very reactive metal, look for an inert hydrocarbon liquid such as kerosene or paraffin as the answer.