Answer
$p(CO)=0.001\ atm$
Work Step by Step
$K_c=[HbCO][O_2]/[HbO_2][CO]$
Fatality: $[HbCO]/[HbO_2]\approx1$
$K_{c,fatal}=[O_2]/[CO]\approx K_{p,fatal}$
$200=0.20/p(CO)$
$p(CO)=0.001\ atm$
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