Question

Match the transition metal ions in Column-I with colour of aquated transition metal ions in Column-Il and choose the correct option.

Column-I Column-II (A) $Zn^{2+}$ (I) Green (B) $V^{2+}$ (II) Violet (C) $Fe^{2+}$ (III) Colourless (D) $Cr^{2+}$ (IV) Blue

• A. (A - ii), (B - iii), (C - iv), (D - i)
• B. (A - iii), (B - iv), (C - i), (D - ii)
• C. (A - i), (B - ii), (C - iii), (D - iv)
• D. (A - iii), (B - ii), (C - i), (D - iv)

Answer 1

Answer: (D)

D

Answer 2

Transition metal ions exhibit color due to d-d transitions, where electrons absorb specific wavelengths of visible light and get promoted to higher energy d-orbitals. The observed color is the complementary color of the absorbed light. This phenomenon requires the presence of partially filled d-orbitals. Ions with completely filled ($d^{10}$) or completely empty ($d^0$) d-orbitals do not undergo d-d transitions and are typically colourless.

Let's analyze each ion:

(A) $Zn^{2+}$

• Electronic configuration of Zn: $[Ar] 3d^{10} 4s^2$
• Electronic configuration of $Zn^{2+}$: $[Ar] 3d^{10}$
• Since the d-orbital is completely filled ($d^{10}$), no d-d transitions are possible.
• Therefore, $Zn^{2+}$ ions are colourless.
• Match: (A) - (III)

(B) $V^{2+}$

• Electronic configuration of V: $[Ar] 3d^3 4s^2$
• Electronic configuration of $V^{2+}$: $[Ar] 3d^3$
• $V^{2+}$ has partially filled d-orbitals ($d^3$), allowing for d-d transitions.
• Aqueous $V^{2+}$ ions are typically violet in color.
• Match: (B) - (II)

(C) $Fe^{2+}$

• Electronic configuration of Fe: $[Ar] 3d^6 4s^2$
• Electronic configuration of $Fe^{2+}$: $[Ar] 3d^6$
• $Fe^{2+}$ has partially filled d-orbitals ($d^6$), allowing for d-d transitions.
• Aqueous $Fe^{2+}$ ions are typically light green in color.
• Match: (C) - (I)

(D) $Cr^{2+}$

• Electronic configuration of Cr: $[Ar] 3d^5 4s^1$
• Electronic configuration of $Cr^{2+}$: $[Ar] 3d^4$
• $Cr^{2+}$ has partially filled d-orbitals ($d^4$), allowing for d-d transitions.
• Aqueous $Cr^{2+}$ ions are typically blue in color.
• Match: (D) - (IV)

Combining the matches: (A) - (III) (B) - (II) (C) - (I) (D) - (IV)

Comparing this with the given options, Option D matches our derived pairs.