If the absolute values of the net charge of the peptide at $pH =2, pH =6$, and $pH =11$ are $\left| z _1\right|,\left| z _2\right|$ and $\left|z_3\right|$, respectively, then what is $\left|z_1\right|+\left|z_2\right|+\left|z_3\right|$ ?
$Hb{O_2} + {H_3}{O^ + }C{O_2} \rightleftharpoons \left( {{H^ + } - Hb - C{O_2}} \right) + {O_2} + {H_2}O$
Release of $O_2$ is favoured when there is