Violet and blue have the high frequencies (thus energy) of visible light. Red will be the least energy but lowest energy. And remember, chlorophyll is green because it reflects green into our eyes. Green is therefore not absorbed, so not used for photosynthesis.
First, let calculate the volume of the rod shaped-bacteria:
S = length of the bacteria * surface of its side = 4.1 * (0.45 *0.45 * 3.14) = 2.6 µm3
Now, let's convert the moles into molecules (with Avogadro's law):
0.0037mol/L = 0.0037 * 6.023 *10^23 = 2.22 *10^21 molecules / L
Now let's convert The volume and the concetrnation into µm3 (molecules / µm3)
1 L = 1 dm3 = 1000 cm3 = 1000000 mm3 = 10^9 µm3
so 2.22 *10^21 molecules / L = 2.22 10^ 12 molecules / µm3
The answer is 2.22 10^ 12 molecules / µm3