Physical Chemistry

- Calamine is a mineral consisting mainly of zinc carbonate, so it is matched with sulphide (I). - Bauxite is an ore of aluminium that contains a large amount of aluminium oxide, hence it is matched with oxide (IV). - Kaolinite is a clay mineral that is primarily made of alumina and silica, which makes it a silicate, hence it is matched with silicate (V). - Cryolite is a mineral used in the production of aluminium, and it contains sodium aluminium fluoride, thus it is a halide, so it is matched with halide (II). Thus, the correct answer is option (1): A-I, B-III, C-I, D-II.

- TiO is widely used in the pigment industry due to its high refractive index and strong opacity. - MnO is commonly used in dry battery cells like alkaline batteries as a depolarizer. - Cu/Ni alloy, often referred to as 'cupro-nickel,' is used in the production of UK 'copper' coins, although they primarily consist of this alloy instead of pure copper. Thus, the correct matching pairs are (i) and (ii), making option (3) the correct answer.

\textbf{Step 1: Understand Physical Equilibrium}
Physical equilibrium occurs when two phases of a substance coexist in dynamic equilibrium, meaning there is no net change in the amount of each phase over time. Examples include:
Solid–liquid equilibrium (e.g., ice and water),
Liquid–vapor equilibrium (e.g., water and steam).
Chemical equilibrium, on the other hand, involves reversible chemical reactions where reactants and products are present simultaneously. Step 2: Analyze Each Option
Option (1):
This is a chemical equilibrium because it involves a reversible chemical reaction between two different molecular species ( and ).
Not a physical equilibrium. Option (2):
This is a chemical equilibrium involving the reversible synthesis of ammonia from nitrogen and hydrogen gases. Not a physical equilibrium. Option (3):
This is a chemical equilibrium involving the decomposition of calcium carbonate into solid calcium oxide and gaseous carbon dioxide. Not a physical equilibrium. Option (4):
This represents the phase equilibrium between liquid water ( ) and water vapor ( ). At a given temperature and pressure, the rates of evaporation and condensation are equal, maintaining a constant concentration of both phases.
This is a physical equilibrium. Step 3: Identify the Correct Option
From the analysis, Option (4) is the only example of physical equilibrium.