Question

Assertion: Chromium oxide and Chromium nitrate are green in color.
Reason: Chromium chloride is violet in color.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Chromium is a chemical element with the symbol $Cr$ and atomic number $24$. It is the first element in group VI. It is a steely-grey, lustrous, hard and brittle transition metal. Chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. Chromium is also highly valued as a metal that is able to be highly polished while resisting tarnishing.

Complete step by step answer:
During the formation of chromium oxide and chromium nitrate, the chromium atom absorbs radiations and the electrons get excited to move to a higher energy level. Chromium atom undergoes various oxidation states during the formation of chromium oxide. Due to the variable oxidation states of chromium, it forms various oxides. In the case of chromium nitrate, there is a transition of one electron and the electron jumps to the higher energy level. When there is a loss of energy from the excited state, the excited chromium atom releases photons of certain wavelength which lie in the visible region of the electromagnetic spectrum, thus, providing colors to the compound. The chromium oxide and chromium nitrate are green in color.
The chromium chloride ($CrC{l_3}$ ) is a purple colored compound and is formed by the attack of three chloride ions on the d- orbitals of the chromium atom. As we can see that both the assertion and reason are true, but the coloration of chromium chloride has no role to explain the coloration of chromium oxide ($Cr{O_3},Cr{O_5}$, etc ) and chromium nitrate (exists as a coordination complex ($[Cr{({H_2}O)_6}]{(N{O_3})_3}.3{H_2}O$ )).

Thus, the correct option is B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

So, the correct answer is option is B.

Note:
Chromium has four unpaired electrons in its d- orbitals and produces colored complexes in which there is a transition in the d- electrons when there is absorption of radiation. All the transition elements show colored complexes by the same mechanism of excitation of electrons to the higher energy levels.