The metal always found in the free state is ____________.
🔬 Understanding Chemical Reactivity and Native Metals
A metal is found in its "free state" or as a "native metal" if it exists in nature in its pure, metallic form, not chemically combined with other elements in an ore. This property is directly related to the metal's chemical reactivity.
Reactivity Series: Metals can be arranged in a series based on how readily they react with other elements like oxygen, water, and acids. Metals at the top (e.g., potassium, sodium) are highly reactive and are never found in a free state. Metals at the bottom are very unreactive and can be found as native metals.
⚖️ Detailed Analysis of the Options
Let's examine the reactivity of the metals listed.
(a) Au (Gold)
Reactivity: Gold is a noble metal, meaning it is extremely unreactive and resistant to corrosion and oxidation. It is located at the very bottom of the reactivity series.
Occurrence: Because of its inert nature, gold is almost always found in its native, metallic state, often as nuggets or flakes in quartz veins and alluvial deposits. The phrase "always found in the free state" is most accurately applied to gold among the common metals.
(b) Ag (Silver)
Reactivity: Silver is also relatively unreactive but is more reactive than gold. It can tarnish by reacting with sulfur compounds in the air.
Occurrence: Silver is often found in its free state, but it is also commonly found in ores like argentite (silver sulfide). Therefore, it is not *always* found in the free state.
(c) Cu (Copper)
Reactivity: Copper is more reactive than both silver and gold. It readily oxidizes to form a greenish patina (verdigris).
Occurrence: While significant deposits of native copper exist, the vast majority of copper is extracted from ores such as chalcopyrite (a copper iron sulfide). It is certainly not always found in its free state.
💡 Study Tips for Metal Reactivity
- The Noble Metals: Remember the "noble metals" (gold, platinum, palladium, etc.) as the ones that are very unreactive and found in their pure form. Gold is the most famous example.
- Reactivity Order: A simplified reactivity order for these three metals is Copper > Silver > Gold. The least reactive one (Gold) is the most likely to be found in its free state.
- Think of Jewelry: Gold jewelry stays bright and shiny for centuries because it doesn't react with the environment. Silver tarnishes (reacts with sulfur). Copper turns green (reacts with oxygen and other elements). This is a real-world example of their reactivity.