Question

The ion which exhibits green colour is:
(A) $C{{u}^{2+}}$
(B) $M{{n}^{2+}}$
(C) $C{{o}^{2+}}$
(D) $N{{i}^{+2}}$

Answer 1

Hint:
Complete step by step solution:
-Transition metals have empty d orbitals except for zinc.
-d orbitals have the same energy level; they are also known as degenerate orbitals.
-When Transition elements undergo formation of complexes or compounds, d orbitals split into two groups having different energy levels.
-Energy differences between both groups are small, so the energy required to jump from lower energy level to higher energy level belongs to the visible range.
-When light from visible range falls on transition element compounds, then electrons of d orbital present in lower energy level absorb energy and jump to higher energy level and transmit.
-Frequency of light depends on which ligand is attached to the transition element.
-In aqueous solution, they exhibit different colours. Zinc has a completely filled d orbital, the solution containing zinc ion is colourless.
The colour observed depends on the frequency of light transmitted or complementary colour to light absorbed.
-So electronic configuration of Nickel is $[Ar]3{{d}^{8}}4{{s}^{2}}$.
-So, in $N{{i}^{+2}}$, two electrons are removed from 4s. it absorbs red colour from visible light and transmits Green colour, so this ion exhibits a green colour.

The ion which exhibits green colour is (D) $N{{i}^{+2}}$.

Note: Incompletely filled d orbitals are involved in the formation of coloured compounds. Ions having completely filled d orbital produce colourless solutions. The colour observed depends on the frequency of light transmitted or complementary colour to light absorbed. The frequency of light depends on which ligand is attached to the transition element.