$10.$ A single$-$molecule microscopy experiment is conducted on a slide with $800$ molecules

each of blue, orange, pink, and purple fluorescent proteins $($BFP$,$ OFP, PFP$,$ and PuFP,

respectively$).$ The results show that $700$ molecules of BFP$,15$ of OFP, $2$ of PFP$,$ and $8$ of

PuFP are bound at a $2$ nM antibody concentration. a$.$ What is the specificity of the antibody

for BFP$?$ b$.$ What is the KD of the BFP$$antibody interaction?