Corrosion

Tarnishing of silver occurs due to its reaction with hydrogen sulfide (H₂S) gas present in moist air. This results in the formation of a black coating of silver sulfide (Ag₂S) on the surface of the silver object: This black layer of Ag₂S is what causes the silver spoon to appear tarnished.

The correct option is (B):

Correct answer: All of these

Explanation:
All the mentioned methods are effective in preventing corrosion:

- Painting: Creates a protective barrier that prevents moisture and oxygen from reaching the metal surface.
- Electroplating: Coats the metal with another metal (like chromium or zinc) to protect it from corrosion.
- Sacrificial electrode: A more reactive metal is used, which corrodes instead of the protected metal (e.g., using zinc to protect iron — called galvanization).

Hence, the correct answer is All of these.

Correct answer: Pyrolusite

Explanation:
Pyrolusite is a mineral that contains manganese dioxide (MnO₂). It is one of the most important ores of manganese.

Here’s what the other minerals contain:
- Galena – Lead sulfide (PbS)
- Cinnabar – Mercury sulfide (HgS)
- Horn silver – Silver chloride (AgCl)

Correct answer: anode

Explanation:
In the process of corrosion of iron (like rusting), the spot where iron corrodes acts as the anode. At the anode, iron loses electrons and gets oxidized to form iron ions:

These electrons travel to another spot (the cathode), where they reduce oxygen in the presence of water. Thus, the corroding spot is the anode.

Corrosion of copper occurs when it is exposed to atmospheric elements, leading to the formation of compounds on the surface. Initially, copper reacts with oxygen and moisture to form copper(I) oxide, which is represented by the chemical equation: 2Cu + O₂ → 2CuO. With continuous exposure to carbon dioxide and water in the atmosphere, copper carbonate is formed. The complete reaction can be summarized as follows:

2Cu + CO₂ + H₂O + O₂ → CuCO₃ · Cu(OH)₂

The final product of copper corrosion when exposed to atmospheric conditions is copper carbonate, also known as patina.
Therefore, the correct answer is: copper carbonate

22-carat Gold is an alloy often used in jewelry, composed primarily of gold and other metals to increase strength and durability while maintaining significant gold content. The term "carat" refers to the purity of the gold alloy, with 24-carat being pure gold. Calculating the components of a 22-carat gold alloy, we find:

• The gold content of 22-carat gold is 22 parts out of 24 parts total, meaning it contains 91.67% gold.
• The remaining 2 parts out of 24 are composed of other metals, not including pure gold.

The most common alloy composition for 22-carat gold, used particularly in jewelry, is gold mixed with copper. This mixture enhances the strength and workability of the gold. Therefore, the composition is:

• 22 parts of Gold + 2 parts of Copper

Rust refers to the corrosion product formed as a result of the oxidation of iron. This happens when iron reacts with oxygen and water. The chemical formula typically associated with rust is , which denotes hydrated iron(III) oxide. This particular formula captures one of the common hydrates formed during this oxidation process:

• Rust is chemically identified as hydrated iron(III) oxide, commonly expressed in its simplest form as .
• When iron is exposed to moisture and oxygen over time, it forms rust in the reaction:
  
  Upon dehydration, converts primarily into .

From the given options, the correct formula for rust is .

In the context of metallurgy, the process of extracting and purifying metals from ores involves several steps. An important component in this process is dealing with impurities. The substance used to remove or mitigate these impurities is known as flux.

Let's examine the provided options:

• Gangue: This term refers to the worthless minerals or earthy substances that surround or are closely mixed with the valuable ore. It is not used to remove impurities.
• Mineral: This is a naturally occurring substance that is typically solid and inorganic, with a distinct chemical composition. Minerals are the source materials for metals, not a means to remove impurities.
• Flux: Flux is a chemical cleaning agent. It is used to bind with impurities and form a slag that can be easily removed from the molten metal, thus purifying the ore.
• Slag: This is the by-product formed after a flux has reacted with impurities. It is not used for removing impurities but is the result of their removal.

Therefore, the correct answer is flux.

The corrosion of silver, also known as tarnishing, is due to the reaction of silver with sulfur-containing compounds in the air, such as hydrogen sulfide ( ). This reaction results in the formation of a black coating of silver sulfide ( ) on the surface of the silver.

During corrosion, a metal undergoes oxidation, which means it loses electrons. So both statements (1) and (2) are true.