b
(b) Plate resistance \(\left(r_{p}\right)=\frac{\delta V}{\delta I}\) (where \(\mathrm{d} \mathrm{V}\) is the change in voltage and \(\delta \mathrm{l}\) is the change in current. At saturation, currelnt \(\delta 1=0 .\) Therefore at saturation \(\left(r_{p}\right)=\frac{\delta V}{0}=\infty\)