Answer:
The wavelength the student should use is 700 nm.
Explanation:
Attached below you can find the diagram I found for this question elsewhere.
Because the idea is to minimize the interference of the Co⁺²(aq) species, we should <u>choose a wavelength in which its absorbance is minimum</u>.
At 400 nm Co⁺²(aq) shows no absorbance, however neither does Cu⁺²(aq). While at 700 nm Co⁺²(aq) shows no absorbance and Cu⁺²(aq) does.
Their is 2 valence electrons
We know that there are 100 cm in 1 m, so we can use this to convert to meters:

Therefore we know that
cm is equal to 2.41 m.
Answer: 55.84L
Explanation: Please see attachment for explanation.