Silver and Gold are metals found as free uncombined elements in the earth's crust, which makes them to be referred to as

Analysis

The question asks for the classification of metals like Silver (Ag) and Gold (Au) based on their occurrence in nature as free, uncombined elements.

Concept Explanation

In chemistry, the reactivity series determines how easily a metal reacts with other substances (like oxygen, water, or acids).

• Highly reactive metals (e.g., Sodium, Potassium) are never found free in nature; they are always found as compounds (ores) because they react quickly with their environment.
• Noble metals (or inert metals) are at the very bottom of the reactivity series. Because they are chemically unreactive (or have very low reactivity), they do not easily lose electrons to form compounds. Consequently, they remain in their metallic state even when exposed to the atmosphere or moisture over millions of years.

Step-by-Step Solution

1. Examine the properties: Silver and Gold are known for their resistance to oxidation and corrosion.
2. Relate to the reactivity series: Because they do not react readily with oxygen or other elements in the earth's crust, they exist in their elemental (native) form.
3. Identify the term: In chemistry, metals that are resistant to chemical attack and oxidation are collectively referred to as noble metals.
4. Evaluate the options: • A. Corrosive metals: Incorrect; these metals are actually resistant to corrosion. • B. Reactive metals: Incorrect; they are the opposite of reactive. • C. Natural metals: While they are found in nature, this is not the scientific term used to describe their chemical inertness. • D. Noble metals: Correct; this is the standard chemical term for metals that are resistant to corrosion and oxidation.

Conclusion

Their low reactivity is the reason they are found in their pure state in the earth's crust.

Exam Tip

Think of "Noble" as "Royal" or "Superior"—just as noble gases (Group 0/8 elements) are unreactive because they have a stable electron configuration, noble metals are "superior" because they refuse to "mix" or react with other elements!