Understanding Metal Reactivity with Oxygen

Metals react with oxygen to form metal oxides. The reactivity of metals towards oxygen varies greatly. Some metals are highly reactive and burn in air, while others react slowly or only at high temperatures. Some very unreactive metals do not react with oxygen even when heated strongly.

Reaction of Common Metals with Oxygen

Let's look at how the metals listed in the options typically react with oxygen:

• Zinc (Zn): Zinc reacts with oxygen when heated to form zinc oxide ($\text{ZnO}$). At room temperature, it reacts slowly to form a protective layer of oxide.
• Aluminium (Al): Aluminium reacts readily with oxygen, forming a thin, tough layer of aluminium oxide ($\text{Al}_2\text{O}_3$). This layer is very stable and prevents further reaction, which is why aluminium appears unreactive despite being quite high in the reactivity series. This process is called passivation.
• Silver (Ag): Silver is a noble metal and is much less reactive than zinc, aluminium, and lead. Silver does not react with oxygen even at high temperatures. However, it is known to tarnish in the presence of sulfur compounds in the air, forming silver sulfide ($\text{Ag}_2\text{S}$).
• Lead (Pb): Lead reacts with oxygen when heated to form lead oxides, such as lead(II) oxide ($\text{PbO}$) and lead(IV) oxide ($\text{PbO}_2$). It also reacts slowly with oxygen and moisture in the air to form a dull coating.

Comparing Reactivity

The reactivity series of metals helps us understand their tendency to react with oxygen. Metals higher in the series are more reactive. Generally, the order of reactivity with oxygen for the given metals is:

Aluminium > Zinc > Lead > Silver

This order indicates that Aluminium is the most reactive among these four, and Silver is the least reactive.

Based on their reactivity, Silver is the metal that does NOT react with Oxygen even at a high temperature.

Revision Table: Metal Reactivity with Oxygen

Additional Information: Reactivity Series and Metal Oxides

The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals higher in the series can displace metals lower in the series from their compounds. Their reactivity with oxygen, water, and acids generally decreases down the series.

Metal oxides formed by reactive metals are usually basic in nature. Some metal oxides, like aluminium oxide and zinc oxide, are amphoteric, meaning they can react with both acids and bases.

Noble metals like Silver, Gold, and Platinum are at the very bottom of the reactivity series and are known for their low reactivity. This is why they are often found in their native state in nature and are used in jewellery.