Matching Explanation: -
(A) Carbon tetrachloride: Used as a fire extinguisher in the past due to its non-flammable properties. Hence, it matches with (III).
(B) Methylene chloride: Commonly used as a paint remover due to its ability to dissolve paint and coatings. Hence, it matches with (I).
(C) DDT: Known for its use as a non-biodegradable insecticide, which has been widely restricted due to environmental concerns. Hence, it matches with (IV).
(D) Freons: These are used as refrigerants and in air conditioners due to their heat absorption and transfer properties. Hence, it matches with (II).
Conclusion: The correct matching is:
• (A)-(III)
• (B)-(I)
• (C)-(IV)
• (D)-(II)
Werner’s coordination theory in 1893 was the first attempt to explain the bonding in coordination complexes. It must be remembered that this theory was put forward before the electron had been discovered by J.J. Thomson in 1897, and before the electronic theory of valency. Werner did not have any of the modern instrumental techniques and all his studies were made using simple experimental techniques. Werner was able to explain the nature of bonding in complexes and he concluded that in complexes, the metal shows two different sorts of valency: primary and secondary. Primary valences are normally ionisable whereas secondary valences are non-ionisable.