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.

Hint: Chromium oxide and Chromium nitrate are green in color. The violet color is also shown by Chromium chloride. The Chromium nitrate also has a deep violet color form. The reason for this color in compounds may be due to d-d transitions or other factors.

Complete answer:
The assertion given is correct. Because both the Chromium oxide and Chromium nitrate are green in color. The Reason given is also true. The Chromium chloride is violet in color.
But the reason for the green color is not mentioned in the Reason given in the question. Instead, it states a fact which does not explain the reason for the Assertion.
So, the answer is option B, both the Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

Additional information: Some of the chemical substances appear to be colored. The reason some of these show various colors is because of the absorption of various energies or wavelengths from the visible light. The wavelength and efficiency of absorption of light depends on the materials' bonding properties. The light absorbed gets scattered or reflected, which our eyes absorb. The reflected spectrum thus defines the color. Some of the colored compounds are used as pigments in paints and so on.
 In all the chemical substances the color is provided by the chromium. The Chromium with oxidation number 3 gives the green color. The compounds which have oxidation number 3 include Chromium oxide and Chromium nitrate. The chromium with oxidation number 2 has blue or violet color, like Chromium chloride.
The reason for color can also be due to the d-d transition.

Note:
Check if the Assertion and Reason are correct. There may be a chance that you may get confused, as some of the compounds show two colors. The compound Chromium nitrate shows green and dark violet color. After that check if the Reason justifies the given Assertion.