$10-17.$ Figure $10-$Pr$17$ shows a breakpoint chlorination curve for a water supply source. $($a$)$ Identify the chlorine dose or the range of doses where the following statements apply: $($i$)$ The free Cl residual is $0\mathrm{.}5$ mg$/$L$.($ii$)$ The combined Cl residual is $2\mathrm{.}0$ mg$/$L$.($iii$)$ The chlorine demand is $4\mathrm{.}0$ mg$/$L$.($iv$)$ When a small increment of chlorine is added, most of it undergoes no redox reaction. $($v$)$ When a small increment of chlorine is added, most of it reacts with N$-$contain$-$ ing compounds. $($vi$)$ When a small increment of chlorine is added, most of it is reduced to Cl$-.($b$)$ What is the chlorine demand when the chlorine dose is $7\mathrm{.}0$ mg$/$L$?$