Question

Match the solutions given in List-I and the colours given in List-II.

	List-I (Aqueous solution of salt)		List-II (Colour)
A.	FeSO₄.7H₂O	P.	Green
B.	NiCl₂.4H₂O	Q.	Light pink
C.	MnCl₂.4H₂O	R.	Blue
D.	CoCl₂.6H₂O	S.	Pale green
E.	Cu₂Cl₂	T.	Pink
		U.	Colourless

• A. A-(P); B-(S); C-(Q); D-(U); E-(T)
• B. A-(S); B-(P); C-(Q); D-(T); E-(U)
• C. A-(S); B-(U); C-(R); D-(T); E-(P)
• D. A-(R); B-(S); C-(P); D-(T); E-(U)

Answer 1

Answer: (B)

A-(S); B-(P); C-(Q); D-(T); E-(U)

Answer 2

The colors of transition metal ions in aqueous solutions are primarily due to d-d transitions, where electrons absorb light in the visible region and get promoted to higher energy d-orbitals. The observed color is the complementary color of the absorbed light. Ions with d⁰ or d¹⁰ configurations are typically colorless as they do not have d-d transitions.

Let's analyze each salt:

A. FeSO₄.7H₂O (Ferrous sulfate heptahydrate)

• This salt contains Fe²⁺ ions.
• Aqueous solutions of Fe²⁺ are typically pale green.
• Therefore, A matches with S.

B. NiCl₂.4H₂O (Nickel(II) chloride tetrahydrate)

• This salt contains Ni²⁺ ions.
• Aqueous solutions of Ni²⁺ are typically green.
• Therefore, B matches with P.

C. MnCl₂.4H₂O (Manganese(II) chloride tetrahydrate)

• This salt contains Mn²⁺ ions.
• Aqueous solutions of Mn²⁺ are typically very light pink or pale pink.
• Therefore, C matches with Q.

D. CoCl₂.6H₂O (Cobalt(II) chloride hexahydrate)

• This salt contains Co²⁺ ions.
• Aqueous solutions of Co²⁺ are typically pink (or rose).
• Therefore, D matches with T.

E. Cu₂Cl₂ (Copper(I) chloride)

• This salt contains Cu⁺ ions.
• The electronic configuration of Cu⁺ is [Ar] 3d¹⁰.
• Since the d-orbital is completely filled (d¹⁰ configuration), there are no d-d transitions possible in the visible region.
• Therefore, aqueous solutions of Cu⁺ are typically colourless.
• Therefore, E matches with U.

Matching the pairs:

A - S B - P C - Q D - T E - U