Would marine algae be able to live below 100 meters with only chlorophyll a?

Probably yes.

Explanation:

Lets check some facts:

1) Chlorophyll a absorbs 2 wavelengths best: 430nm (blue) and 662nm (red) (see first figure)

2) Sea water absorbs some wavelengths of color spectrum as it gets deeper. A diver can experience this in first hand with the absence of colors. Red and violet is the first two that is cannot be seen anymore (see second figure) . But blue light can reach up to 200 meters but there is a catch: with higher turbidity this can be reduced. So; since chlorophyll a can absorb blue light marine algae can survive with only chlorophyll a up to 200 meters in oceans (see third figure).

answer: i don't know

explanation:

you need to provide a picture, otherwise i can't tell you.

if you can provide one, i'd be more than happy to you with this!

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.