Question

Which of the following is not a chromophore.
A.$-N=N-$
B./$-NO$
C.$-N{{O}_{2}}$
D.$-N{{H}_{2}}$

Answer 1

We know that the chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.

Complete answer:
As we know that the term chromogen is applied to a colorless chemical compound that can be converted by chemical reaction into a compound which can be described as colored and chromophore is the portion of a molecule's structure which absorbs visible light photons, causing the molecule to have color and An auxochrome is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. When an organic compound absorbs the radiation in the visible part of the electromagnetic spectrum, it appears to be colored.
Some groups do not impart color but when present along with chromophore groups are responsible for deepening the color of the compound. These are electron-donating groups and are known as auxochromes. Examples of auxochrome groups are: $-\overset{\centerdot \centerdot }{\mathop{N}}\,{{H}_{2}},~~-\overset{\centerdot \centerdot }{\mathop{N}}\,HR,~~-\underset{\centerdot \centerdot }{\overset{\centerdot \centerdot }{\mathop{O}}}\,H$
Therefore, the correct answer is option D.

Note:
Remember that the presence of an auxochrome in the chromogen molecule is essential to make a dye. However, if an auxochrome is present in the Meta position to the chromophore, it does not affect the color. An auxochrome is known as a compound that produces a bathochromic shift, also known as red shift, because it increases the wavelength of absorption.