If coil is open then $L$ and $R$ become

When coil is open, there is no current in it, hence no flux is associated with it, ie, $\phi=0$. Also, we know that flux linked with the coil is directly proportional to the current in the coil, ie, $\quad \phi \propto i$ or $$ \phi=L i $$ where $L$ is proportionality constant known as self-inductance. $\therefore$ $$ L=\frac{\phi}{i}=0 $$ Again since $i=0$, hence, $R=\infty$.