The electronic excitation energy required for a molecule to absorb light in the visible region depends on the specific molecule and its electronic structure. The visible region of the electromagnetic spectrum ranges from approximately 400 nm violet to 700 nm red . To calculate the energy associated with a specific wavelength, we can use the formula:E = h * c / where E is the energy, h is the Planck's constant 6.626 x 10^-34 Js , c is the speed of light 2.998 x 10^8 m/s , and is the wavelength in meters.Optical properties of a molecule that absorbs light in the visible region include:1. Absorption spectrum: The absorption spectrum shows the wavelengths of light absorbed by a molecule. A molecule that absorbs light in the visible region will have an absorption spectrum with peaks in the 400-700 nm range.2. Color: The color of a molecule is related to the wavelengths of light it absorbs. If a molecule absorbs light in the visible region, it will appear colored because it reflects or transmits the complementary colors of the absorbed wavelengths. For example, if a molecule absorbs light in the blue region around 450 nm , it will appear yellow-orange, which is the complementary color of blue.3. Fluorescence and phosphorescence: Some molecules that absorb light in the visible region can also emit light through fluorescence or phosphorescence. Fluorescence occurs when a molecule absorbs light and then quickly releases the energy as light of a longer wavelength lower energy . Phosphorescence is similar to fluorescence, but the energy release is slower, leading to a longer-lasting glow.4. Photochemical reactions: Absorption of light in the visible region can cause molecules to undergo photochemical reactions, where the absorbed energy leads to chemical changes in the molecule. These reactions can result in the formation of new molecules or the breaking of chemical bonds.