Paramagnetic substances are substances which are attracted by magnetic field. This is because they require very little amount of energy for electron transition. The energy can be easily provided by visible light. The colour observed corresponds to the complementary colour of light absorbed.

Due to presence of unpaired electron transition of electron is possible in transition they absorb visible light so they are coloured..

Introduction:
Paramagnetic substances are materials that are weakly attracted to magnetic fields due to the presence of unpaired electrons. Unlike diamagnetic substances, which are repelled by magnetic fields, paramagnetic substances exhibit a slight magnetization in the direction of the applied field. One of the interesting characteristics of paramagnetic substances is their ability to exhibit color, which is attributed to the presence of unpaired electrons.

Explanation:
When light passes through a material, it interacts with the electrons present in that material. The interaction between light and electrons determines the color we perceive. In paramagnetic substances, the presence of unpaired electrons causes unique electronic transitions that lead to the absorption of specific wavelengths of light. This absorbed light corresponds to certain colors, resulting in the substance appearing colored to our eyes.

Electronic Transitions:
In paramagnetic substances, unpaired electrons occupy different energy levels within the atom or molecule. When light, which consists of photons with specific energy levels, interacts with the substance, it can be absorbed by the unpaired electrons. This absorption leads to electronic transitions, where electrons move from lower energy levels to higher energy levels. The energy difference between these levels corresponds to a specific wavelength of light, and the substance absorbs that particular color from the incident light.

Color Perception:
The color we perceive is determined by the wavelengths of light that are not absorbed by the substance. For example, if a substance absorbs light in the blue region of the spectrum, it will appear yellow because it reflects or transmits the complementary color of blue, which is yellow. The absorbed light energy causes the electrons to undergo transitions, and the substance appears colored due to the specific wavelengths of light it absorbs and the wavelengths it reflects or transmits.

Examples:
1. Copper (II) sulfate (CuSO4): The presence of unpaired electrons in the copper atom results in the compound appearing blue. Copper (II) sulfate absorbs light in the orange region of the spectrum, giving it a blue color.

2. Potassium permanganate (KMnO4): The compound appears purple due to the presence of unpaired electrons in the manganese atom. Potassium permanganate absorbs light in the green region of the spectrum, resulting in the compound appearing purple.

Conclusion:
The presence of unpaired electrons in paramagnetic substances leads to unique electronic transitions, which cause the absorption of specific wavelengths of light. The absorbed light corresponds to certain colors, resulting in the substance appearing colored to our eyes. Understanding the relationship between unpaired electrons and color in paramagnetic substances helps explain their vibrant appearances and contributes to our understanding of their magnetic and optical properties.