A solution absorbs light with wavelengths corresponding to red, yellow and green light - AQA - A-Level Chemistry - Question 31 - 2017 - Paper 3

To determine which ion is most likely to be in the solution based on the absorption of light, we need to consider the colors absorbed and the corresponding wavelengths.

Red light has a wavelength of approximately 620-750 nm, yellow light around 570-590 nm, and green light about 495-570 nm. If the solution is absorbing these colors, it is likely to transmit colors from the blue/violet end of the spectrum.

Among the options provided:

1. Cr2O7^{2−}(aq) - Typically has orange to red color and hence would not absorb red, yellow, or green effectively.
2. Fe^{2+}(aq) - Generally appears pale green to light blue, absorbing colors in the red range; thus does not meet our criteria.
3. Fe^{3+}(aq) - This ion tends to absorb light in the green region, making it less likely to be the right choice since it would transmit red and yellow.
4. Cu^{2+}(aq) - This ion is known to present a blue color in solution and effectively absorbs light in the red, yellow, and green regions, making it likely to be found in a solution primarily absorbing these wavelengths.

Therefore, the ion that is most likely to be in the solution is Cu^{2+}(aq).