Reaction centre in Photosystems of higher plants
Someone else too had asked your question no. 2. here Photosystem 1 and 2; P680/P700; Chlorophyll a/b

The answer basically quotes Molecular Biology 4 ed. by Lodish as follows.

"The chlorophylls in the two reaction centers differ in their light-absorption maxima because of differences in their protein environment."

[I could've just commented this but I can't locate add comment option on your post. Am new here.]