Question

Of the ions Zn2+ , Ni2+ and Cr3+ (atomic number Zn = 30, Ni = 28, Cr = 24):

• A. Only Zn2+ is colourless and Ni2+ and Cr3+ are coloured.
• B. All three are colourless.
• C. All three are coloured.
• D. Only Ni2+ is coloured and Zn2+ and Cr3+ are colourless.

Answer 1

Answer: (A)

Only Zn2+ is colourless and Ni2+ and Cr3+ are coloured.

Answer 2

Valence shell electron configuration of 30Zn2+ is 3d1ŗ 4sŗ. As there is no unpaired electrons for d–d transition, the solution of ions will be colourless.

Valence shell electron configuration of 28Ni2+ is 3d8 4sŗ. As there are 2 unpaired electrons, there is d–d transition of electron, so the solution of ions will be coloured.

Valence shell electron configuration of 24Cr3+ is 3d3 4sŗ. As there are 3 unpaired electrons, there is d–d transition of electron, so the solution of ions will be coloured.