In basic chemistry of metals, which highly reactive metal is commonly stored under kerosene oil to prevent it from reacting with air and moisture?

Introduction / Context:
Different metals vary widely in their reactivity with air, water, and other substances. Highly reactive metals can corrode or react violently if they come into contact with moisture or oxygen. To store such metals safely, chemists often keep them under oil so that air and water cannot reach them. This question asks which metal, among the options given, is so reactive that it is commonly stored under kerosene oil in school laboratories and basic chemistry demonstrations.

Given Data / Assumptions:

• Options include copper, sodium, platinum, and gold.
• Sodium is an alkali metal; copper, platinum, and gold are less reactive or noble metals.
• Kerosene oil does not mix with water and forms a barrier against air.
• We assume standard school laboratory safety practices.

Concept / Approach:
Sodium is a soft, silvery alkali metal that reacts vigorously with water, producing sodium hydroxide and hydrogen gas, often with enough heat to ignite the hydrogen. It also reacts with oxygen in air to form oxides and peroxides. Because sodium is so reactive, it cannot be safely left exposed to air and moisture. Instead, it is stored under kerosene or other mineral oils, which cover the metal and prevent contact with water and oxygen. Copper is less reactive and can be stored in air without special precautions. Platinum and gold are noble metals that resist corrosion and do not require storage under oil.

Step-by-Step Solution:
Step 1: Recall that sodium is an alkali metal placed in Group 1 of the periodic table and is highly reactive with water and oxygen. Step 2: Remember that when sodium is dropped into water, it reacts vigorously, releasing hydrogen gas and forming a strong alkali (sodium hydroxide). Step 3: Understand that to prevent accidental contact with moisture and air, sodium is stored under kerosene oil in sealed containers. Step 4: Compare this with copper, which tarnishes slowly but does not react violently with water and is commonly stored in air. Step 5: Note that platinum and gold are very unreactive, often called noble metals, and are used in jewellery and laboratory equipment because they do not corrode easily. Step 6: Conclude that sodium is the metal that must be stored under kerosene oil.

Verification / Alternative check:
Chemistry textbooks regularly illustrate the reactivity series of metals, showing that alkali metals like lithium, sodium, and potassium are among the most reactive. Laboratory safety sections warn that sodium and potassium should be stored under oil to avoid dangerous reactions. Demonstrations in school often show sodium reacting with water, skittering on the surface and sometimes igniting. In contrast, copper is widely used in electrical wiring and utensils without special storage, and platinum and gold are valued precisely because they resist corrosion. This confirms that sodium is the correct answer.

Why Other Options Are Wrong:
Copper, a relatively unreactive transition metal, does not require storage under kerosene; it forms a protective oxide or patina but does not react violently with water.
Platinum, a noble metal with high resistance to corrosion, is extremely unreactive and is safely stored in air; it is used in jewellery and laboratory apparatus.
Gold, a noble metal often used in jewellery, is also highly resistant to corrosion and tarnish, so there is no need to store it under kerosene.

Common Pitfalls:
Students may confuse "valuable" or "rare" with "reactive," assuming that metals like gold need special storage because they are precious. In reality, gold’s value partly comes from its low reactivity and resistance to corrosion. Another common error is to forget that alkali metals are at the top of the reactivity series. A simple memory aid is that Group 1 alkali metals such as sodium and potassium are so reactive that they must be kept under oil, whereas noble metals like gold and platinum are stable in air.

Final Answer:
The highly reactive metal commonly stored under kerosene oil is Sodium, a very reactive alkali metal that reacts vigorously with water.