(i) The shaded area $\mathrm{AOB}$ indicates "Dissavings".
(ii) At point $\mathit{B}$, saving is zero and total income is equal to total consumption.
It means:
$\mathrm{C}=\mathit{y}$
$\mathrm{APC}=\frac{\mathit{c}}{\mathit{y}}=\frac{\mathit{y}}{\mathit{y}}=1$
$\mathrm{APS}=1-\mathrm{APC}$
$=1-1=0$
$\mathrm{APS}=0$
Point $\mathit{B}$, average propensity to save is zero