A solution of \(\mathrm{Co}^{2+}\) ions appears red when viewed under white light. Which of the following statements is true about the solution? (A) A spectrophotometer set to the wavelength of red light would read a high absorbance. (B) If the solution is diluted, the amount of light reflected by the solution will decrease. (C) All light with a frequency that is lower than that of red light will be absorbed by it. (D) Electronic transmissions within the solution match the wavelength of red light.

The color we observe in a substance under white light is a result of the wavelengths of light the substance reflects. Therefore, if the Co^2+ ions appear red under white light, they are absorbing all other colors and reflecting red light. Now let's evaluate each statement. (A) A spectrophotometer measures the amount of light that a sample absorbs. The light not absorbed is what gives the substance its color. Thus, a spectrophotometer set to the wavelength of red light would read a low absorbance because the solution reflects rather than absorbs red light. (B) If the solution is diluted, the concentration of ions that absorb light decreases. This means that more light -- not less -- is likely to pass through the solution, which would make the solution look lighter, not darker. Therefore, the amount of light reflected by the solution would increase, not decrease.(C) The light with a frequency lower than that of red light includes all the colors such as orange, yellow, green, blue, indigo, and violet. However, we see the color red because all the other colors are being absorbed and only red light is being reflected. So this statement is not correct.(D) The color of the light absorbed is determined by the energy differences between electronic energy levels in the atom/ion. Co^2+ ions absorb light in the blue/green part of the spectrum which corresponds to the energy difference between its electronic energy levels, and it reflects the complementary color, which is red. Thus, this statement is correct.